Conceptual advances in the biological sciences are marked by the applica tion of new techniques and experimental strategies. Nowhere has this ge neric principle been more apparent than in the study of testicular cells, as judged by the evolution of themes presented at the Testis Workshop over the past 23 years. Like its predecessors, the 1995 Testis Workshop was structured to offer fresh insights and approaches for understanding the mechanisms of spermatogenesis and steroidogenesis. The chapters pre sented in this book emphasize three aspects of testicular cell function: first, the molecular analysis of the cell cycle; second, examination of the cell cycle, including the function and identification of specific macromolecules that direct the proliferation and differentiation of germ cells; and third, the development of Leydig cells and the role of specific macromolecules in the formation of testicular steroids. Each chapter is based on a lecture presented at the XIIIth Testis Work shop held on March 30 to April 1, 1995, at the Radisson Plaza Hotel in Raleigh, North Carolina. The selection of topics reflects the recommenda tions of the workshop'S organizing committee. Sincere thanks are due to the speakers who agreed to lecture and prepare chapters."

Each new volume of this publication brings the privilege of expressing some of my thoughts on subjects of interest to its readers. In the past year or so public concern about environmental and societal dangers has largely turned to those of cosmic proportion-Chernobyl, the thinning ozone layer, AIDS, and the like-and thankfully our subject matter has been allowed a respite. Even the miniepidemic of craniofacial and other malformations caused by the retinoid antiacne drug Accutane made no headlines. Incidentally, this might have been a tragedy of far greater proportions had it not been nipped in the bud by the historical ground work that quickly permitted it to be recognized as due to an environ mental teratogen-the sort of fact the public and authorities inadequately appreciate. But there is a warning connected with this abeyance of media focus on teratological matters. Disquiet over cosmic imbalances will sub side as they are corrected or horrendous projections fail to materialize, and even cures for dread infectious diseases, or Puritan revolution in terdicting such plagues, will be forthcoming, and these things will occur long before congenital malformations are no more. And as the year-in and year-out recurrence of over 100,000 an nual births of seriously malformed infants in the United States alone continues to force itself on the public consciousness, we can expect a heightened demand that "a cure" be found, because "if we can land a man on the moon, if we can prevent polio, why can't we . . ."

Polycystic ovarian disease, or polyfollicular ovarian disease, as Dr. Fut terweit prefers to call it, is a disease of uncertain etiology and for which numerous modes of therapy have been advanced. Understanding of its pathophysiology should shed light on factors regulating normal ovarian function; the converse is also true. Recent years have brought about great understanding of the neuro endocrine regulation of gonadal function, as well as of factors in the microenvironment of the ovary which affect its function. It is also ap preciated that cases classified as polycystic ovarian disease actually rep resent a clinical and pathological spectrum which may reflect the effects of diverse etiological factors. In the present volume, Dr. Futterweit presents the fruits of his long interest in and extensive experience with this disease. He thoroughly and thoughtfully reviews the vast amount of basic and clinical information that has been garnered with regard to this condition over the past decade. The numerous theories that have been advanced to explain its etiology are presented in balanced fashion, in addition to a hypothesis, which is well formulated and amenable to clinical testing. His clinical interests and judgment are well represented by his presentation of the diverse manifestations of this condition, the approach to proper diagnosis, and the available therapeutic options. Patients with this disease represent diagnostic and therapeutic prob lems in a situation where manifestations of disease may lead to major emotional stress."

The perimenopause is an extremely important time in a woman's life. In a similar but reverse sequence to puberty, it signals a change in ovarian status. Although some women pass through this transition without symptoms or concern, for many women, the perimenopause, which can last several years, is of great concern. Symptoms of estrogen deficiency, menstrual irregular ity, concerns over changes in mood, as well as reproductive concerns lead to anxiety and frustration. Because it is poorly understood, many clinicians are equally frustrated in finding ways to help their patients and question the appropriateness and/or need for treatment. This Serono Symposia USA, Inc., meeting was designed to help address some of these issues from both a basic science and a clinical perspective, and to provide a forum for discussion. The waning of ovarian function can be divided into two events that are dissociated: gametogenic and endocrine failure. Thus, the symposium was divided into three parts to address these two phenomena and to discuss treatment options. An outstanding international group of clinicians and investigators assembled to first address oocyte depletion and possible markers. Next the complex endocrine changes were discussed as well as the physiologic consequences of these changes. This included a discussion of hot flushes, bone and cardiovascular changes, menstrual irregularity, mood disturbances and depression, and anatomical changes in the ovary and breast. The third part of the symposium addressed treatment options, both in terms of symptoms as well as reproductive and fertility concerns."

Ultrasonic surgical techniques were first used by Dr. Kelman in the 1960s to fragment cataracts through a 2-mm incision allowing for minimally invasive surgery. The results from this procedure stimulated the development of a larger, move powerful ultrasonic unit that was used in neurosurgery. This instrument allowed the neurosurgeon to selectively remove tumor tissue with decreased blood loss and tissue trauma. The ability now of ultrasonic equipment to selectively fragment, irrigate, and aspirate tissue with minimal coagulation effect spurred its rapid use in surgery on the liver, spleen, kidney, and other intra-abdominal organs. This instrument has been invaluable in ovarian cancer cytoreduction and intricate segmental organ resection. The newest technical developments include electro cautery capability built into the hand piece and extended hand pieces for laparoscopic surgery. The impetus for assembling this volume has been to provide an extensive review of the field of ultrasonic surgery as it has currently developed including principles, equipment features, and surgical tech niques. It is hoped that the information will be of use to physicians in training and surgeons in practice. The book takes a multidisciplinary approach with chapters authored by a diversity of subspecialists in gen eral surgery, urology, surgical oncology, and gynecologic oncology. Each chapter contains basic information on surgical techniques. Together, these chapters cover surgery of the GI tract, kidney, liver, and lower genital tract, and present a number of personal approaches."

Since the awarding of the Nobel Prize to Drs. Guillemin and Schally iJ) 1971 for isolation and chemical characterization of gonadotropin releasing hormone, we have experienced a remarkable period of growth of interest in this hormone. The last 20 years have been characterized by a swift translation of basic science discovery into clinical utility. Approval of GnRH and its analogs for treatment of prostate cancer, endometriosis, of ovulation indicate the range and precocious puberty and for induction of these agents. of usefulness In order to bring together the leaders in the basic and clinical science of GnRH, a conference was organized on "Modes of Action of GnRH and GnRH Analogs" and held in Scottsdale, Arizona, February 26 to March 2, 1991. The presentations, given as chapters in this volume, show both the advances in the body of information in this discipline and the efforts underway to reduce basic science to clinical practice. The audience was a combination of representatives from universities, government, industry, and physicians in practice. The lively discussions and insightful questions indicated the interest in the topics discussed and frequently served to catalyze planned interactions of the meeting participants. The organizers are grateful to the speakers and poster presenters for their contributions and for the timely preparations of the manuscripts included in the present volume. We are also thankful to the staff of Serono Symposia, USA, for the organizational skills and support that allowed the meeting organizers to focus on the science and medicine presented.

Why Efforts to Expand the Meaning of "Teratogen" Are Unacceptable Disagreement about nomenclature in teratology is not new. Dissent even about the very fabric of the discipline-what congenital malformations consist of-has often been voiced. Time, instead of resolving such diffi culties, has sometimes worsened them. For example, in the past it was agreed that congenital malforma tions are abnormalities of structure present at birth, but differences of opinion concerning where the line between normal and abnormal was to be drawn prevailed. It was obvious that, in order to discover the causes of congenital malformations and cast strategies for their prevention, it would be necessary to have knowledge of the baseline of their frequency, and that this required uniformity of definition of terms. Since malfor mations of primary social concern are those having grave outcomes (and are, paradoxically, also the commonest ones), it is logical that such condi tions were the first consideration of investigators and were the defects whose frequency was considered to comprise the required baseline.

Proceedings of the NATO Advanced Study Institute, San Miniato, Italy, September 2-13, 1985

Current Perinatology, II, explores the most recent major research techniques utilized in the evaluation, diagnosis, and management of the high-risk mother and her newborn. The volume should be a major reference for pediatricians, perinatologists, and neonatologists, as well as for nurses and allied health personnel closely involved with the care of the high-risk mother, fetus, and newborn. Topics presented include perinatal Doppler; Doppler echocardiography of the human fetus; invasive fetal assessment by fetal blood sampling; prediction, prevention, and treatment of preterm labor; percutaneous umbilical blood sampling and intravascular fetal therapy; current and future perspectives for fetal genetic diagnosis; current concepts of substance abuse during pregnancy; newer methods of diagnosis and treatment of neonatal sepsis; clinical applications of neonatal pulmonary function testing; and current management of hypoplastic left heart syndrome. Discussions of stabilization and transportation of the critically ill obstetric patient and of pain management in the neonatal intensive care unit will be of interest to both physicians and nurses.

Trophoblast cells coordinate the activities of maternal and embryonic tissues by secreting hormones, cytokines, and various growth factors that selectively and specifically gain access to maternal and embryonic compartments. Abnormalities associated with trophoblast cell growth, differentiation, or function result in impaired embryonic development. Understanding the complexities of the trophoblast cell signaling system was the focus of the Serono Symposia, USA conference entitled Tropho blast Cells: Pathways for Maternal-Embryonic Communication, held August 6-9, 1992, in Las Vegas, Nevada. The conference was designed to provide a forum for morphologists, cell biologists, endocrinologists, and molecular biologists and for scientists investigating primate, ru minant, and rodent trophoblast biology. An important outcome of the conference was the communication achieved between basic scientists and clinicians. This volume represents the contributions of the invited symposium speakers. The opening keynote address of the conference was entitled "Chorio carcinoma and the Embryo" and was presented by G. Barry Pierce, M. D., Centennial Distinguished Research Professor of the University of Colorado School of Medicine. The address is not represented in this volume, but deserves a special comment. Dr. Pierce's scientific con tributions have significantly influenced our understanding of trophoblast cells. Dr. Pierce, together with Dr. A. Rees Midgley, identified the origin of syncytial trophoblast cells of the primate placenta and discovered that these cells were responsible for the production of chorionic gonadotropin (J Exp Med 1962;115:289-94; Am J Pathol 1963;43:929-43; and Science 1963;141:349-50)."

Medicine is changing at a speed never witnessed before in history. With each passing year, medical technology achieves the capacity to provide cures and improve treatments that even a short time before were difficult to con ceptualize and impossible to provide. Reproductive technology personifies this concept perhaps better than any other field of medicine. The 1990s have seen an explosion in endoscopic and ambulatory procedures, the application of molecular biology to clinical conditions, and the refinement of assisted reproduction to allow third parties (donors and surrogates) into the process of family building. More than ever before, comprehensive medical care requires a team approach. However, the team comprises not only medical and scientific personnel, but also mental health professionals, lawyers, and ethicists. This integrated and multidisciplinary approach to medical care will become even more necessary as medical capabilities continue to develop faster than society can respond. This book reflects such an approach. It is based on a Harvard Postgraduate Course in June 1990 entitled Infertility in the 1990s: Technological Advances and Their Psychosocial Implications that was sponsored by the Faulkner Centre for Reproductive Medicine. The first half of the course was directed by Drs. M. Seibel, A. Kiessling, and C. Richards. The second half of the course was directed by Dr. M. Seibel, J. Bernstein, R. N. and S. Levin, LICSW."

The pregnant host is at risk for any of the viral diseases her nonpregnant counterpart acquires. Additionally, pregnancy heightens our concerns regarding specific viral diseases be cause of their potential for enhanced adverse effects on both maternal and fetal well-being. All too often the obstetrician relinquishes responsibility for the management of the gravida infected by a viral pathogen, and those expert in infectious diseases are confounded by the influence of pregnancy on these conditions. A major goal of this textbook is to narrow the gap between the two aforementioned management dichotomies in the virally infected pregnant woman. Weare at the infancy of our understanding of viral infections in pregnancy. The current and anticipated advancements are due in large part to a burgeoning oftechnological achievements in the areas of immunodiagnostics, molecular biology, and pharmacotherapeutics. Our in utero diagnostic capabilities, both invasive and noninvasive, have also allowed us new opportunities to study the effects of various maternal infectious disease processes on the developing fetus. New insights have been recognized pertaining to the maternal-fetal interface, the placenta, in that this structure is now acknowledged to function as both a mechanical and an immunological barrier to vertical transmission of infection. These observations suggest that there will be an outpouring of new data in the next several years that clinicians will need to master to maintain an appropriate level of expertise in the care of their patients.

Breast Care: A Clinical Guidebook for Women's Primary Health Care Providers presents the expertise and protocols of the renowned Breast Diagnostic Center at USC School of Medicine's Department of Obstetrics and Gynecology. A user-friendly reference for the primary care physician, this book details the management of both benign and malignant breast diseases. Topics include: * the clinical examination and instruction for self-exam * mammography for both screening and diagnosis, management of the abnormal mammogram * lactation and breast feeding * diagnosis and treatment of lumps, cysts, fibroadenomas * fine-needle aspiration and ultrasound guided tissue core needle biopsy * evaluation and management of mastalgia * menstrual and hormonal therapy effects on the breast * the cosmetically treated breast * guidelines for follow-up and surveillance An important section on consultation and referrals reviews the roles of the radiologist, oncologist, and surgeon and provides the primary care physician with the information necessary to counsel the patient on the myriad aspects of multidisciplinary treatment planning. The text includes more than 100 illustrations and algorithms -- with 16 in color -- as well as "Practice Guides" which organize the key practice points, signs, and symptoms. This is a must-have handbook for all providers of health care to women.

For many years now, our understanding of the somatotrophic and reproduc tive axes has evolved essentially independently, both fields of study reaching a highly advanced, although far from complete, level of under standing. Along the way, however, it became apparent that in some circumstances the reproductive and somatotrophic axes may be inter dependent. Inklings to this effect were at times feeble and at other times more convincing. Among those inklings are the clinical recognition by pediatric endocrinologists of the apparent association between isolated GH deficiency and delayed puberty, as well as of the apparent permissive, pUberty-promoting property of GH. Equally important is a body of experi mental studies establishing the ovary of multiple species as a site of GH reception and action. Arguing against an essential role for GH in the reproductive process is the observation that individuals who have GH resistance of the Laron variety are fertile arid that isolated GH deficiency does not constitute an absolute barrier to the attainment of sexual maturation and fertility. The intraovarian insulin-like growth factor (IGF) hypothesis proposes that IGFs may serve as amplifiers of gonadotropin action. Although the dependence of intraovarian IGFs on systemic GH action has never been unequivocally demonstrated, that leap of faith has often been made. The intraovarian IGF hypothesis serves as the rationale for the adjunctive use of GH in the induction of ovulation."

Originally published in 1982 Obstetrics and Gynaecology in Tudor and Stuart England traces the development of obstetrics and gynaecology over the past two centuries. Between the 16th and 18th century midwifery passed from a female mystery, employing traditional medicines and superstitions, to a scientifically-based clinical skill, with both gains and losses to the patient. The case-mortality was high enough to make the increasing involvement of male surgeons socially acceptable, despite sexual taboos. Thus, as scientific knowledge of anatomy and physiology developed and was applied in the form of new techniques, so the midwives, who had less opportunity and inclination to acquire the new knowledge and skills, lost esteem and by the mid-eighteenth century were increasingly relegated to the service of the poor. The book also examines ideas about sexuality, menstruation, conception, pregnancy and lactation and shows how the views of society about femaleness, marital relations and the management of pregnancy and childbearing were influenced by these notions.

Thoroughly illustrated, this second edition provides the primary care physician with detailed information on the most commonly encountered clinical situations and the most frequently asked questions. The chapters address everything the primary care physician will regularly face and will need to know about the breast, pregnancy, sexually transmitted diseases, contraception, infertility, gynecologic cancers, urogynecology and gynecology.

The importance of osteoporosis in the United Kingdom as a cause of death and disability is now well recognised. There are in excess of 200,000 osteoporotic-related fractures in the UK per annum asso ciated with an estimated cost of GBP942,000,000. Following hip fracture it is known that about 50% of patients are unable to live indepen dently and about 20% of such patients die within the first 6 months. These figures, compelling as they are, reflect poorly on current medical practices which manifestly have failed to identify patients with low bone density at risk of fracture. The hope is that the techni cal advances which have enabled bone mineral density, and other allied indices, to be measured with high precision and accuracy offers the chance of identifying patients at risk of fracture and guiding the clinician to make treatment decisions which may reduce the patients' risk of fracture. In the UK, services for identifying patients at risk of fracture are still in their infancy and are not uniformly available throughout the country. This situation is, however, likely to improve particularly fol lowing the publication of the Royal College of Physicians report "Osteoporosis -clinical guidelines for prevention and treatment" and the recognition in "Our Healthier Nation" that osteoporosis pre vention should be included as a target to achieve a reduction of 20% in accidents by 2010.

Since its inception in 1976, the overall goal of the Ovarian Workshop has been to bring together biologists from various disciplines so that they may collectively achieve a better understanding of the latest developments and define important problems in ovarian physiology. The Ovarian Workshop, which was pioneered by Dr. A. Rees Midgley, has developed into a major biennial meeting for investigators in the ovarian field. Largely as a consequence of advances in technology, especially in mo- lecular biology, progress in the area of gene expression and signal transduc- tion has been rapid. The Eighth Ovarian Workshop focused on two major topics: (1) the expression of hormonally and nonhormonally controlled genes involved in the functional and morphological differentiation of the cells forming the ovary and (2) the signaling mechanisms by which endogenous and exogenous hormones and cytokines affect ovarian differentiation and steroidogenesis. The Eighth Ovarian Workshop, held on the campus of Maryville College in Maryville, Tennessee, July 12 to 14, 1990, was again generously funded and coordinated by Serono Symposia, USA. I would especially like to thank Dr. Lisa Kern of Serono for her expert help in organizing this meeting. The board of directors of the Eighth Ovarian Workshop consisted of Drs. Eli Adashi, JoAnne Fortune, Anne Hirshfield, Aaron Hsueh, Julia Lobotsky, Gordon Niswender, David W. Schomberg, Richard Stouffer, and Jerry Strauss. Their valuable advice and the important roles they played in the planning of the scientific program are gratefully acknowledged.

practitioner up to date on the various aspects of conditions and diseases considered to be sexually transmitted. REFERENCES 1. Crissey JT, Denenholz DA: Development of the modern forms and concepts of syphilis. Clin Dermatol, 2(1):1-10, 1984. 2. Panconesi E, Mazzi M: The day syphilis came. Int 1 Dermatol, 23:284-286, 1984. 3. Washington AE, Johnson RE, Sanders LL: Chlamydia trachomatis infections in the United States: What are they costing us? lAMA, 257:2070-2074, 1987. 4. Bulkley LD: Syphilis in the Innocent. New York: Bailey and Fairchild, 1894. 5. Syphilis: Major perinatal killer. Med World Trib, 28(16):2, 1987. 6. Renshaw DC: Management of impotence. I. Psychological considerations. Clin Therap, 9:142-148,1987. Acknowledgments. We are very grateful to our teachers for the stimulation they provided in our studies of dermatology and sexually transmitted diseases. We partic ularly acknowledge the impetus given by Herman Beerman, M.D., Emeritus Professor of Dermatology, University of Pennsylvania School of Medicine, Philadel phia. Our office staffs have been particularly helpful, and we would like to recognize the contributions of Mrs. Carmela Ciferni. Lastly, this book was conceived through the inspiration of Dr. Jerry Stone, late Senior Medical Editor of Springer-Verlag, New York. Philadelphia, Pennsylvania LAWRENCE CHARLES PARISH Vienna, Austria FRIEDRICH GSCHNAIT Contents Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v Contributors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Xl . . . . . . . . . . . . . . . What are Sexually Transmitted Diseases? Chapter 1 History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 . . . . . . . . . . . . . LOIS Y. MATSUOKA Chapter 2 Definition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 . . . . . . . . . . . . HARRY L. ARNOLD, JR. Diseases Chapter 3 Syphilis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 . . . . . . . . . . . . . JOHN THORNE CRISSEY Chapter 4 Endemic Treponematoses . . . . . . . . . . .. . . . . . . . . . . . . . . . 32 . . ."

Intrauterine Growth Restriction: Aetiology and Management will be the first book to focus exclusively on this extremely important and common complication of pregnancy. There have been many recent developments in our understanding of the aetiology and pathogenesis of the condition as well as in screening, monitoring and therapy. This book is unique in that it covers both the aetiology and pathogenesis as well as clinical management and also includes sections on definitions and potential future advances. Every aspect is covered by an international expert which will provide the reader with a valuable insight into this condition.

In the last few years rapid advances have been made in reproductive medicine, making it necessary for those involved to regularly update their knowledge. The purpose of this book is to describe the state of the art in this field, making it possible for the reader to gain an orientation among all the diagnostic and therapeutic potentials of modern reproductive medicine in order to advise patients fully. Chapters from the fields of gynecology, and reproductive medicine in a specific sense provide knowledge about these subjects. Authors of international standing have contributed chapters on their specialties. These chapters together form a book describing the state of the art in the diagnosis and therapy of sterility in gynecology and andrology.

During recent decades, it has been firmly documented that chlamydiae are com mon and important pathogens in humans and animals. In humans, chlamydiae are known to cause trachoma (which is still one of the major blinding diseases in the world) and are also one of the most common etiological agents of sexually transmitted diseases and the sequelae thereof, such as infertility. In the last few years, it has also become evident that chlamydiae, i.e., the so-called TWAR agents, are common respiratory tract pathogens. Chlamydiae are also important pathogens in birds and lower mammals, in whom they cause a variety of infectious conditions, a spectrum which has in creased every year. Some of these infections occur as zoonoses, e.g., psit tacosis/ornithosis and, as recently discovered, abortion. Know ledge of the molecular biology and immunobiology of chlamydiae has expanded rapidly during recent years. Insight into the pathophysiology of chla mydial infections has also increased, and new methods for the diagnosis of chlamydial infections have been introduced. The importance of establishing control and preventive programs for chla mydial infections has become obvious in order to combat the present chlamydial epidemic. We hope that this book can usefully serve those who want to increase their general knowledge of Chlamydia and that it can act as a handbook and reference source for those involved in chlamydial research as well as for those working with chlamydial infections in medical and veterinary clinical disciplines, includ ing clinical laboratories."

The purpose of this series of volumes is to present a comprehensive view of the complications that result from the use of acceptable diagnostic and thera peutic procedures. Individual volumes will deal with iatrogenic complications involving (1) the alimentary system, (2) the urinary system, (3) the respiratory and cardiac systems, (4) the skeletal system and (5) the pediatric patient. The term iatrogenic, derived from two Greek words, means physician-in duced. Originally, it applied only to psychiatric disorders generated in the patient by autosuggestion, based on misinterpretation of the doctor's attitude and comments. As clinically used, it now pertains to the inadvertent side effects and complications created in the course of diagnosis and treatment. The classic categories of disease have included: (1) congenital and developmen tal, (2) traumatic, (3) infectious and inflammatory, (4) metabolic, (5) neoplastic, and (6) degenerative. To these must be added, however, iatrogenic disorders a major, although generally unacknowledged, source of illness. While great advances in medical care in both diagnosis and therapy have been accomplished in the past few decades, many are at times associated with certain side-effects and risks which may result in distress equal to or greater than the basic condi tion. Iatrogenic complications, which may be referred to as "diseases of medical progress," have become a new dimension in the causation of human disease."

The concept of the foeto-placental unit as an integrated endocrine organ has been defined recently by many in vivo studies at the 17th- 20th week of gestation. A functioning foeto-placental unit is necessary for most of the increased oestrogen production of pregnancy and for the provision of glucocorticoids and aldosterone to the foetus. Neither the foetus nor the placenta alone have the necessary enzyme systems for the synthesis of these groups of steroids. However, when the foetus and placenta function as a unit, all of the enzyme systems are present for the synthesis of these steroids from circulating cholesterol. The placenta, but not the mid-gestation foetal adrenal, can synthesize physiologically significant amounts of pregnenolone from circulating cholesterol. Part of the pregnenolone is converted to progesterone in the placenta by the 3 -HSD system (absent in the foetus). The progesterone is transferred to the foetus where it is transformed by C-II, C-17, C-18 and C-21 hydroxylases (all absent in the placenta) to cortisol, corticosterone and aldosterone. Pregnenolone transferred from the placenta to the foetus undergoes 171X-hydroxylation, side chain splitting and sulfurylation (absent in the placenta) and is converted to DHAS. The DHAS may undergo 161X-hydroxylation (absent in the placenta) in the foetal liver and be transported to the placenta as 161X-OH-DHAS. There it is subjected to a neutral steroid sulfatase (absent in the foetus) and is converted to oestriol by action of the 3 -HSD system and the aromatizing enzyme system."