MULTIPLE PREGNANCY doc

DEFINITIONS, ASSOCIATION, INCIDENCES AND IMPORTANCE Multiple pregnancy involves more than one embryo (fetus) in any one gestation. Two independent mechanisms may lead to multiple gestation: segmentation of a single fertile ovum (identical, monovu- lar, or monozygotic) or fertilization of separate ova by different spermatozoa (fraternal or dizygotic) multiple pregnancy. In the development of twins (the most frequent higher-order ges- tation), monozygotism is constant (ϳ2.3–4/1000 deliveries), whereas dizygotism has certain predispositions. Dizygotic twinning is inher- ited as a recessive autosomal trait via the female descendants. The father’s being a twin has little influence on the rate of twinning in his offspring. Race is of special importance: blacks have the great- est incidence of dizygotic twins (about 50/1000 births in Western Nigeria), whites are intermediate, and Asians have the fewest (ϳ1–2/1000 births in Japan). Other factors influencing dizygotism include greater maternal height or weight, increasing maternal age (peaks at 35–45 years), and white mothers of blood group O or A. In developed countries, two of the major causes of multiple gestation are cessation of oral contraception and artificial ovulation induc- tion. The latter is of particular concern for higher-order multiple gestations (triplets and above) are increasingly common (1.2- to 2-fold increase in developed countries) as a result of assisted re- productive technologies (ART). Although these pregnancies are not at significantly increased risk from the ART, they are at exceptional risk for immature or premature delivery and other morbidity and mortality associated with higher-order multiple gestations. In the heterogeneous population of the United States, slightly .30% of twins are monozygotic, and nearly 70% are dizygotic (Fig. 12-1). In such a population, a useful estimate of the natural fre- quency of multiple gestation is that twinning occurs ϳ12 per 1000 births (1:88). Each increase in birth number may then be estimated 12 MULTIPLE PREGNANCY CHAPTER 367 Copyright 2001 The McGraw-Hill Companies. Click Here for Terms of Use. BENSON & PERNOLL’S 368 HANDBOOK OF OBSTETRICS AND GYNECOLOGY by raising the ratio 1:88 to the exponential of the birth number mi- nus 1. For example, triplets occur 1:88 (3Ϫ1 ϭ 2) ϭ 1:7744; quadru- plets occur 1:883 3 ϭ 1:681,472. In multiple births, males predominate (but more die early). About 75% of twins are of the same gender. Both are males in ϳ45% of cases, and both are females in ϳ30%. Maternal morbidity and mortality are much higher in multiple than in singleton pregnancy. There is increased frequency and sever- ity of anemia; increased occurrence of urinary tract infection; more preeclampsia-eclampsia, hydramnios, and uterine inertia (overdis- tention); and a greater chance of hemorrhage (before, during, and after delivery). The perinatal mortality rate of twins is 4–6 times higher—and for triplets much higher again—than for singletons because of prematu- rity and associated difficulties. Indeed, as the number of fetuses rises, their average size and length of gestation decrease. Twins are deliv- ered, on average, at ϳ36 weeks, triplets at ϳ32 weeks, and quadru- plets at Ͻ30 weeks. Moreover, intrauterine growth retardation (IUGR) is more common in all multiple gestations (as opposed to sin- gletons). Congenital abnormalities of all organ systems are as high as 18% among twins (considering both monozygotic and dizygotic). Other perinatal risks of multiple gestations include abnormal presen- tation and position, hydramnios, hypoxia because of cord prolapse (ϳ4%, 5 times more common in multiple pregnancy), placenta pre- via, and premature separation of the placenta after the first twin or operative manipulation. Collision, impaction, and interlocking of twins are additional critical but uncommon complications (Figs. 12-2, 12-3, and 12-4). Because of maternal and perinatal risk, many authorities FIGURE 12-1. Placental variations in twinning. (After Potter.) recommend that no less than qualified obstetricians care for twins and that maternal–fetal consultation be utilized. Additionally, triplet and higher birth order risk is such that maternal–fetal specialists should be involved in, or provide their care. CHAPTER 12 MULTIPLE PREGNANCY 369 FIGURE 12-2. Locked twins. FIGURE 12-3. Both twins presenting by the vertex. BENSON & PERNOLL’S 370 HANDBOOK OF OBSTETRICS AND GYNECOLOGY Monozygotic multiple fetuses are far more likely to be jeopard- ized than dizygotic twins. For example, monozygotic twins have 3 times the incidence of serious congenital abnormalities compared to double-ovum twins. Conjoined twins and enhanced early loss of one or both fetuses (probably two thirds of all implanted multiple gestations) result in a single birth. Moreover, a parasitic fetus with- out a heart (fetus acardiacus, complicating ϳ1%) is also a potential problem of monozygous twinning. Other unique monozygotic com- plications include placental vascular shunts resulting in the twin-to- twin transfusion syndrome (to some degree complicates 5–35%), in which the smaller but cardiomegalic twin pumps its arterial blood into the lower pressure venous system of the larger, plethoric, and macrosomic twin. Cord abnormalities, more common in monozy- gous twins, include two-vessel cords and velamentous cord inser- tion (7% incidence). Cord entanglement in a single monoamniotic sac may occur, and this leads to a ϳ50% loss. Monozygotic twins are smaller and are more likely to die in utero than dizygotic twins. This may be because a single (monochorionic) placenta is less ef- ficient than a fused dichorionic placenta. The time of segmentation is crucial to the outcome of monozy- gotic fetuses. Division before the morula and differentiation of the FIGURE 12-4. One vertex and one breech presentation. CHAPTER 12 MULTIPLE PREGNANCY 371 FIGURE 12-5. Amniotic membranes of twins. BENSON & PERNOLL’S 372 HANDBOOK OF OBSTETRICS AND GYNECOLOGY trophoblast (day 5) lead to separate or fused placentas with two chorions and two amnions. Division after trophoblastic differentia- tion but before amnion formation (5–10 days) is the pattern of two thirds of all monozygotic twins. This results in a single pla- centa, a common chorion, and two amnions. Division after amnion differentiation (10–14 days) leads to a single placenta with one chorion and one amnion. Division Ͼ14 days results in incomplete twinning. Division just before that (8–14 days) may lead to con- joined (Siamese) twinning. Monozygotic multiple gestations share the same genetic features (e.g., blood group, histocompatibility, and basic karyotypes). There- fore, skin grafting and organ transplantation are possible and be- come the ultimate test of monozygotic vs. dizygotic twinning. Monozygotic twins are termed identical, but they often have con- siderable phenotypic variation. Dizygotic (fraternal) twins may be of the same or different genders and bear only the resemblance of brothers or sisters. They may or may not have sufficiently similar genetic features to serve as organ donors for each other. Examination of the placenta and membranes assists in zygosity determination. At delivery, careful inspection and dissection of the placenta(s) and membranes, particularly the membraneous T-septum or dividing membrane between the twins, may reveal microscopic evidence of the probable type of twinning. Monozygotic twins have a thin septum made up of two amniotic membranes only (no chorion and no decidua). Indeed, ϳ1% of monozygotic twins are monoam- niotic. By contrast, dizygotic twins have a thick septum composed of two chorions, two amnions, and intervening decidua (Fig. 12-5). In some circumstances, it is necessary to resort to definitive genetic testing to determine monozygosity or dizygosity. The early diagno- sis of twins is mandatory, and assessment of the placenta is the key. CLINICAL FINDINGS The clinical suggestions of multiple pregnancy include the following: ● A uterus larger than expected for the duration of pregnancy (Ͼ4 cm than anticipated); ● Excessive maternal weight gain not explained by eating or edema; ● Hydramnios; ● Iron deficiency anemia; ● Maternal reports of increased fetal activity; ● Eclampsia-preeclampsia; ● Uterus containing Ն3 large parts or multiple small parts; ● and simultaneous auscultation or recording of two fetal hearts varying Ͼ8 beats per min and asychronous to the maternal heart. LABORATORY FINDINGS Commonly encountered laboratory findings in multiple pregnancy include: abnormal elevation of maternal hCG and/or alpha- fetoprotein, moderate reduction in Hct (also Hgb and RBC count, i.e., iron deficiency anemia), blood volume increased over normal pregnancy values, and an increased incidence of glucose intoler- ance. Cervicovaginal secretion of fetal fibronectin (Ffn) is a sensi- tive predictor of preterm delivery in twins, but has low specificity. Thus, Ffn is best used in conjunction with other criteria (e.g., sono- graphic evaluation of cervical length). Currently, there is little Ffn data for higher-order multiples. SONOGRAPHY Sonography is vital in modern management of multiple gestations. Areas of utility include: assisting in zygosity determination, detect- ing and assessing fetal anomalies, determination of growth, assess- ing amniotic fluid, determining well being, management of antena- tal testing, and caring for uncommon complications. Therefore, a standardized approach to sonographic evaluations is useful. EARLY SONOGRAPHY Sonography (no later than the early second trimester) assists in de- termination of chorionicity. Multiple pregnancy may be demon- strated by vaginal ultrasonography before 6 weeks, and multiple pregnancy should be routinely detected by other scanning methods at Ͻ8 weeks. A pitfall of multiple gestation sonography, particu- larly those done at Ͻ6 weeks, is both undercounting and over- counting fetuses. Sonographic visualization of the chorion(s) can be assessed as early as 6–7 weeks (after LMP), with dichorionic being visualized earlier. Although reliable imaging of the amnion is not usually pos- sible before the 9–10th week. This determination is important be- cause of the disproportionate outcomes related to chorionicity and amnionicity. Differential findings include: placental masses, septal thickness, “twin peak” sign, as well as fetal gender. At 16–20 weeks, a detailed sonographic anatomic survey screens for congenital anomalies and provides a baseline for further testing. CHAPTER 12 MULTIPLE PREGNANCY 373 BENSON & PERNOLL’S 374 HANDBOOK OF OBSTETRICS AND GYNECOLOGY Serial sonographic examinations may vary by chorionicity. Sonography for dichorionic pregnancies are often started later (26 weeks v. 23 weeks) and subsequently, performed less frequently (4 weeks v. 3 weeks) than monochorionic twins, although optimal schedules have not been articulated. Serial examinations are useful in determination of growth patterns, assessing amount of amniotic fluid, determining fetal position, ascertaining placental maturation, and a host of other useful information. Serial songraphic assessment of cervical length as well as screening for cervical funneling is a useful adjunct in management of multiple gestations. Premature cervical shortening and cervical funneling both indicate the potential for premature labor and de- livery. Prior to or at the onset of labor, sonography is useful in plan- ning management (see the discussion that follows). DIFFERENTIAL DIAGNOSIS Single large pregnancy, hydramnios, hydatidiform mole, abdominal or pelvic tumors complicating singleton pregnancy, and compli- cated multiple gestation (e.g., triplets) must all be considered in the diagnosis of multiple gestation. TREATMENT PREVENTION OF MULTIPLE PREGNANCY Currently there are few possibilities for preventing multiple gesta- tion, but those known follow. Use of a barrier type of contracep- tion for the first cycle off oral contraceptives may prevent fertil- ization of multiple ova. Administering clomiphere initially, if ovulation is to be induced results in fewer multiple gestations. How- ever, dizygous twins still occur in 5%–10% of clomiphene-stimu- lated cycles. Avoiding the use of human menopausal gonadotropin therapy unless the proper dosage can be established and daily sonog- raphy is available for ovulation monitoring assists in lowering mul- tiple gestation. Selective reduction of fetuses (i.e., selective elimi- nation) is a new and controversial technique of elimination of one or more fetuses. This technique employs ultrasonic-guided methods for reducing the number of fetuses, with the rationale that intact survival of a few is better than nonintact survival of many. Initial reports support this approach in selected cases. AVOIDING MATERNAL COMPLICATIONS IN MULTIPLE PREGNANCY A thoughtful approach is necessary for the mother with multiple gestations. This plan begins with early diagnosis of multiple preg- nancy. This goal may be achieved by obtaining sonography (ideally on all and certainly on questionable pregnancies) no later than 12–16 weeks. A high-protein, high-vitamin diet; with no limitation of weight gain assists in prevention of fetal intrauterine growth retar- dation. Dietary supplements demonstrated to be useful in multiple gestations include: a prenatal vitamin per day, folic acid of 1.0 mg per fetus per day, supplemental iron preparations as indicated by hemogram and calcium to a total intake of 1500 mg/day benefi- cially influences birth weight. Because of the number of potential problems, it is common to examine the patient with multiple pregnancy more often than most during pregnancy (individualized, but in most cases at least twice as often). Physical activity is usually limited to ensure adequate uter- ine blood flow (e.g., cancel regular exercise programs). Frequent rest periods are initiated after the 24th week (e.g., 1 week of bedrest at 26 weeks and again at 32–33 weeks). Ultrasound examinations and blood counts are obtained more frequently. Ultrasound exami- nations for growth progress may be useful monthly from diagnosis until the 32nd week, when both ultrasonography and BPP on each fetus may be useful on a weekly basis. Cervical length sonography may be performed as often as every other week in the latter half of pregnancy. Given the risk, consideration is given to deliver all patients with multiple pregnancy in a tertiary medical facility if possible. Psy- choprophylaxis is often stressed, and the patient introduced to a sup- port group. Additionally, patients find literature concerning multi- ple gestation and preterm birth prevention education helpful. At the time of delivery, increased blood loss may be anticipated (hemor- rhage is 5 times increased over singletons). Thus, seeking donors acceptable to the patient in advance may be worthwhile. In cases where one fetus delivers untenably early (e.g., 22 weeks), some now recommend delaying delivery of the remaining fetuses (especially if membranes are intact) in an attempt to decrease morbidity and mortality in the remaining fetuses. Although the delayed delivery of remaining fetuses improves prognosis, there is no consensus re- garding technique or enough cases to demonstrate true statistical relevance. In sum, care of the mother with a multiple pregnancy re- quires enhanced sensitivity to, as well as frequent assessment of, maternal symptoms and cervical status. CHAPTER 12 MULTIPLE PREGNANCY 375 BENSON & PERNOLL’S 376 HANDBOOK OF OBSTETRICS AND GYNECOLOGY PREVENTION OF FETAL COMPLICATIONS OF MULTIPLE GESTATION Details concerning identifying congenital anomalies are noted pre- viously (see “Imaging”), as are techniques to maximize fetal growth (see “Maternal Care”). Preventing early preterm delivery is an ob- jective best realized through maximizing maternal antenatal care (as above). The utilization of fetal fibronectin screening may be use- ful in detection of preterm labor. Utilization of home uterine activ- ity monitoring, salivary estriols, and other modalities may be con- sidered. Cervical cerclage may delay preterm birth in selected cases. Indeed, some now recommend this in triplet and higher-order ges- tations. Further study is necessary, however, prior to recommend- ing this approach. Tocolytic drugs to prevent early birth may be effective (Chap- ter 11); however, these agents must be used with great care in mul- tiple gestation because of possible maternal pulmonary edema. Ap- propriate fetal therapy is initiated if early delivery is anticipated (Chapter 11). ASCERTAIN FETAL PROBLEMS It is important to ascertain fetal problems early. Certainly, some of these may be determined by repeated sonography to screen for fe- tal defects, IUGR, fetus-to-fetus transfusion syndrome, and fetal well-being. Antenatal diagnosis is used as indicated. The twin-to- twin transfusion syndrome is usually manifest in monozygous twins by discordant fetal growth (a difference of Ͼ20%) and one fetus having polyhydramnios while the other has oligohydramnios. Indi- vidual testing for pulmonary maturity studies is utilized (if neces- sary). If selective reduction is an option, the patient may be referred to an appropriate center. LABOR During labor, special vigilance is warranted. Labor is conducted with full preparations for cesarean section, should the need arise. This includes: starting IV lactated Ringer’s solution with a large- bore needle, obtaining a complete blood count, and blood type and crossmatch for a minimum of 2 units packed red blood cells or whole blood. Maternal and fetal oxygenation is enhanced by mask or nasal prong oxygen therapy (7 liters/min). Sonography assists in ascertaining the fetal presentations. In practice, this nearly always [...]...CHAPTER 12 MULTIPLE PREGNANCY 377 TABLE 12-1 DELIVERY SITUATIONS ACCORDING TO PRESENTATION OF TWINS Situation A B C Twin A Twin B % Vertex Vertex Nonvertex Vertex Nonvertex Other (any) Ͼ40 ϳ40 ϳ20 involves one of the... in Table 12-1 In most obstetric units, only twins are considered for vaginal delivery All those of higher birth orders, with the exception of certain centers familiar with vaginal birth of high-order multiples, should be delivered by cesarean section All fetuses should be separately electronically monitored In the United States, if fetal monitoring of this type is not primarily available, consideration . chorionicity. Multiple pregnancy may be demon- strated by vaginal ultrasonography before 6 weeks, and multiple pregnancy should be routinely detected by other scanning methods at Ͻ8 weeks. A pitfall of multiple. all be considered in the diagnosis of multiple gestation. TREATMENT PREVENTION OF MULTIPLE PREGNANCY Currently there are few possibilities for preventing multiple gesta- tion, but those known. MATERNAL COMPLICATIONS IN MULTIPLE PREGNANCY A thoughtful approach is necessary for the mother with multiple gestations. This plan begins with early diagnosis of multiple preg- nancy. This