Adverse perinatal outcome of twin pregnancies according to chorionicity: review of the literature

Discordant growth in twins

Discordant growth in twins contributes significantly to rates of perinatal morbidity and mortality. These rates vary according to chorionicity, timing of onset and severity. We have reviewed English language literature in Medline since 1980. It is clear that diagnosis of discordant growth has improved due to the use of serial ultrasound examination. Following the detection of differences in fetal size, diagnosis is facilitated by umbilical artery and fetal Doppler studies. Management options vary according to chorionicity, timing of onset and umbilical-fetal Doppler studies. The mode of delivery in discordant twins remains controversial. We conclude that ultrasound surveillance of twin gestations, combining serial biometry and selective Doppler studies, is effective in the recognition of significant intrauterine growth restriction in co-twins. Differences in etiology and management underscore the importance of establishing chorionicity routinely as soon as twin gestation is diagnosed.

The sonographic diagnosis of chorionicity

The differentiation between mono- and dichorionic placentation in twin pregnancies is of clinical importance because of the significant difference in perinatal morbidity and mortality between the two, and the increased surveillance indicated in monochorionic gestations. Application of ultrasonography has enabled very precise prenatal determination of chorionicity. While this is best performed in the first trimester when accuracy approaches 100%, even in the third trimester, using a composite cascade of available sonographic features, accuracy has been reported to approach 97%. While two clearly separate placentae or discordant fetal gender conform to dichorionicity, in most twin pregnancies other features need to be assessed to determine chorionicity. The presence of the 'lambda' or the 'T' sign in the presence of a single placenta, best determined in the first trimester, is the most reliable indicator of chorionicity, with measurements of the inter-twin membrane thickness and counting of the membrane layers being less reliable. In this article, we review the sonographic features that help in the accurate depiction of chorionicity.

Effects of antenatal betamethasone administration on fetal heart rate and behavior in twin pregnancy

The efficacy of antenatal corticosteroid therapy in reducing the incidence of respiratory distress syndrome in twin pregnancy is controversial. The corticosteroid levels achieved with the current regimen might not be high enough to reach both siblings. In singleton fetuses, maternal betamethasone administration causes transient reductions in fetal heart rate (FHR), FHR variability, and body and breathing movements. We performed a prospective study to determine whether there are similar effects of betamethasone on FHR and behavior in preterm twin pregnancy and whether the effects occur similarly in both twin members. Eighteen women who were carrying twins received optimal corticosteroid treatment. Simultaneous recordings were made on twins before (day 0), during (days 1-2), and after (days 3-4) corticosteroid therapy using separate cardiotocography and ultrasound machines. Betamethasone administration was associated with significant transient decreases in basal FHR (day 1), FHR variability (days 2 and 3), and body and breathing movements (day 2). The overall changes in twins were similar to those previously found in singleton pregnancies. There was a high degree of association of response to betamethasone among individual members of twin pairs. The betamethasone-induced effects were unrelated to fetal sex, positioning, chorionicity, and discordance in size, but there was an effect of gestation on FHR. We conclude that the current regimen of antenatal corticosteroids used in preterm twin pregnancies results in observable physiologic and behavioral changes in twin pairs irrespective of their composition. This provides evidence that the achieved betamethasone levels are high enough to reach the compartment of either twin member.

The Utility of fFN for the Prediction of Preterm Birth in Twin Gestations

OBJECTIVE

To determine the sensitivity, specificity, and positive predictive value (PPV) of fetal fibronectin (fFN) and to determine its usefulness, in conjunction with selected other clinical assessment measures, in the prediction of preterm birth for women with twin gestations.

DESIGN

A prospective, descriptive, longitudinal design.

SETTING

An obstetrical high-risk clinic that received patient referrals from several surrounding communities in central Texas.

PATIENTS/PARTICIPANTS

Forty-eight women identified with twin gestations prior to the 22nd week of pregnancy; primarily of Hispanic ethnicity.

MAIN OUTCOME MEASURES

A substantial number of outcome variables were assessed in this study. In the present report, data derived from weekly assessments for the identification of the presence of fFN, the diagnosis of bacterial vaginosis, and the measurement of cervical length were reviewed for their relationship to prematurity, birth weight, birth weight discordancy and placental chorionicity.

RESULTS

The relative risk of birth prior to 35 weeks gestation, fetal death, or discordance of twin birth weights of greater than 20% was 2.22 (CI: 1.09, 4.55, P < 0.015) when fFN was found to be positive at any weekly testing after 22 to 24 weeks gestation (sensitivity 76.82%, specificity 58.33%, PPV 66.7%). The presence of fFN was most highly predictive of preterm birth when performed during the 24th to 28th gestational week. Shorter cervical lengths were highly correlated with preterm birth (r = -0.6). An association between bacterial vaginosis and preterm birth was not demonstrated in this sample.

CONCLUSION

Sampling for the presence of fetal fibronectin can be easily accomplished by RNs in labor triage units and by advanced practice nurses in outpatient settings. The identification of fFN, particularly during the 24 to 28 weeks gestational time frame, is highly predictive of preterm birth, and particularly so for women with twin gestations.

Adrenocortical responsiveness is blunted in twin relative to singleton ovine fetuses

Twin fetuses experience much higher rates of perinatal mortality/morbidity than age- and weight-matched singletons. Across species, the prepartum increase in fetal plasma cortisol is responsible for maturing a number of systems in preparation for birth and the immediate postnatal period. In sheep, it is known that basal adrenocortical function is delayed in twins relative to singletons. Thus, it could be argued that relative immaturity in twins may explain their increased susceptibility to stress in the perinatal period and their relatively poor perinatal outcome. However, whether adrenocortical responsiveness to stress is also diminished in the twin fetus and whether the fetal cardiovascular, metabolic and endocrine defences to acute stress are comparatively weak in the twin fetus is unknown. This study investigated the effect of twinning on adrenocortical responsiveness to either the physiological stress of acute hypoxaemia or to an exogenous ACTH test, and on the fetal cardiovascular, metabolic and endocrine responses to acute hypoxaemic stress. Twenty Welsh Mountain sheep fetuses were chronically instrumented (1-2% halothane) at 121 +/- 3 days of gestation (term is ca 145 days) with amniotic and vascular catheters and with a transit-time flow probe around a femoral artery. The animals were divided into two groups based upon fetal number (singletons, n= 10; twins, n= 10), as determined at surgery. At 130 +/- 2 days, a 1 h episode of acute, isocapnic hypoxaemia (to reduce carotid P(O(2)) to 12 +/- 1 mmHg) was induced in all fetuses by reducing the maternal inspired O(2) fraction (F(IO(2)); 9% O(2) in N(2)). Fetal cardiovascular variables were recorded at 1 s intervals throughout the experimental protocol and arterial blood samples taken at appropriate intervals for biophysical (blood gases, glucose, lactate) and endocrine (catecholamines, vasopressin, cortisol, ACTH) measures. At 133 +/- 2 days a 2.5 microg bolus dose of synthetic ACTH (Synacthen; Ciba Pharmaceuticals, UK) was injected i.v. into eight of the singleton and six of the twin fetuses to determine adrenocortical steroidogenic sensitivity to exogenous ACTH. Under basal conditions, twins had lower plasma cortisol concentration, arterial blood pressure and femoral blood flow relative to singleton fetuses. Twins responded to acute hypoxaemia with similar pressor and vasopressor responses compared to singleton fetuses. However, the rate pressure product, an index of myocardial work, tended to decrease during hypoxaemia in twins, in contrast to the increase observed in singletons. Similar increases in the fetal plasma concentrations of ACTH, AVP, noradrenaline and adrenaline were observed during hypoxaemia in both groups; however, both the increments in fetal plasma concentration of cortisol in response to acute hypoxaemia and to exogenous ACTH were blunted in twins relative to singletons. This study shows that basal adrenocortical function as well as adrenocortical responsiveness is blunted in the twin relative to the singleton fetus. Further, the mechanism for adrenocortical blunting resides at the level of the adrenal cortex rather than higher up the axis. Relative adrenocortical immaturity in the twin fetus may reflect a specific endocrine adaptation to prolong gestation in multiple ovine pregnancies; however, such an adaptation does not affect the cardiovascular, metabolic or endocrine defence responses to acute hypoxaemia in the twin fetus.

Why and how should multiple pregnancies be prevented in assisted reproduction treatment programmes?

Although most professional societies have issued guidelines to diminish the number of embryos to be transferred during assisted reproductive techniques, the incidence of multiple pregnancies remains unacceptably high. The burden of morbidity and mortality seems to increase substantially with each fetus in a multiple gestation. As a result, there has been growing debate on the need to prevent multiple pregnancies. The infertility specialists who can solve the infertility problem are usually shielded from the complications of multiple pregnancies. If they were involved in the delivery and, more particularly in the care of multiple pregnancies (both financially and socially), their attitude would probably change. IVF centres should gradually reduce the mean number of embryos per transfer in terms of the cost:benefit ratio. A further reduction to one single embryo per transfer in good cases would be similarly acceptable. Laboratory expertise is of vital importance, especially in terms of embryo culture, embryo selection, and freezing and thawing techniques in embryo transfer programmes for reducing the number of transferred embryos.

Mean arterial pressure in very low birth weight (801 to 1500 g) concordant and discordant twins during the first day of life

OBJECTIVE

To determine retrospectively mean arterial pressure (MAP) for stable and unstable concordant and discordant very low birth weight (VLBW: 801 to 1500 g) twins during the first 24 hours of life.

BACKGROUND

Morbidity and mortality are much higher for extremely low birth weight (ELBW < or =800 g) than for VLBW twins. Recently, we reported MAP trends and reference values in concordant and discordant ELBW twins. No comparable information is available for VLBW infants.

DESIGN

Retrospective cohort study.

METHODS

We studied 48 sets of concordant and 40 sets of discordant (birth weight difference > or =20%) consecutively born VLBW twins. Stable patients were defined as having umbilical cord hemoglobin > or =14 g/dl, nonacidotic blood gases, never treated for hypotension and survived at least 7 days. MAPs (Torr) were measured by oscillometry in 3163 and by transducer via umbilical artery in 2028 instances.

RESULTS

Concordant and discordant twins were similar in demographics, history of twin-twin transfusion (TTTX), antenatal steroids, chorioamnionitis, pre-eclampsia, cesarean delivery, cord hemoglobin, normal head ultrasounds or I to II intracranial hemorrhage (97 and 99%) and neonatal mortality (4 and 5%), but were different in incidence of preterm labor (83 and 58%), birth weight (1227 and 1509 g) and gestational age (GA) (30 and 32 weeks). In all, 66 (69%) concordant twins and 61 (76%) discordant twins were stable. Stable concordant twins, whether small or large, had comparable MAP on admission that increased to 24 hours. Twins of < or =32 weeks GA had lower MAP throughout than those of > or =33 weeks GA. Although their mean birth weights were similar (1262 and 1274 g), 23 stable concordant males had significantly higher MAP than 43 concordant females. Stable discordant twins were divided into 31 small (1241 g) and 30 large (1845 g); their MAPs were different (p<0.05): 35 and 39 (admission), 35 and 39 (1 hour), 36 and 46 (6 hours), 38 and 41 (12 hours), 40 and 41 (18 hours) and 42 and 42 (24 hours) Torr. In all, 88% of small discordant twins were IUGR and 91% of large discordant twins had normal growth. TTTX syndrome occurred in 12 monochorionic sets. Nine of 12 donors were IUGR while 10 of 12 recipients had normal growth. Four of 12 donors had grades III to IV intracranial hemorrhage, eight donors and all 12 recipients had normal ultrasounds. Although their cord hemoglobin levels were similar, donor and recipient MAPs were higher than in any other group and, opposite to concordant and discordant twins, their values decreased from birth to 24 hours.

CONCLUSION

In stable concordant, stable discordant, and small and large discordant twins, MAP correlates with birth weight, GA and postnatal age, and increases during the first 24 hours. In recipient and donor twin-twin transfusion infants, MAP is higher throughout and declines over time.

Antenatal factors associated with significant birth weight discordancy in twin gestations

OBJECTIVE

The purpose of this study was to evaluate factors that are associated with significant birth weight discordancy.

STUDY DESIGN

As a part of an ongoing collaborative study of twins, maternal and fetal data were obtained from the medical records of twin gestations at eight medical centers. The study population was divided into groups by difference in birth weight discordancy (>or=20%, >or=25%, and >or=30%)

RESULTS

Severe birth weight discordancy was associated with fetal growth deceleration by 20 to 28 weeks (adjusted odds ratio, 4.90; 95% CI, 3.15-7.64) and between 28 weeks to birth (adjusted odds ratio, 3.48; 95% CI, 1.72-7.06). Antenatal bleeding (adjusted odds ratio, 1.86; 95% CI, 1.08-3.21), preeclampsia (adjusted odds ratio, 1.70, 95% CI, 1.21-2.41), and monochorionicity (adjusted odds ratio, 2.35, 95% CI, 11.71-3.23) were also associated with birth weight discordancy.

CONCLUSION

These data demonstrate the importance of the early diagnosis of placental chorionicity, because monochorionicity is associated with a 2-fold increase in birth weight discordancy in twin gestations.

Risk factors for intrapair birth weight discordance in twins

OBJECTIVES

To determine the risk factors for birth weight discordance in twins.

METHODS

We used the United States (1995-97) Matched Multiple Birth File (n = 294 568) to assess the association between birth weight discordance and maternal sociodemographic, pregnancy and infant characteristics.

RESULTS

Eighty-four per cent of the twins were 0-19% discordant, 11.1% were 20-29% discordant, 3.4% were 30-39% discordant, and 1.8% were > or = 2 40% discordant. The risk factors for birth weight discordance for same-sex twins were eclampsia (odds ratio (OR) 1.39,95% confidence interval (CI) 1.20, 1.61), pre-eclampsia (OR 1.31, 95% CI 1.24, 1.38), pre-existing hypertension (OR 1.32, 95% CI 1.12, 1.56), diabetes (OR 1.13, 95% CI 1.04, 1.24) and certain congenital anomalies. For opposite-sex twins, the risk factors for birth weight discordance were pre-eclampsia (OR 1.17, 95% CI 1.09, 1.27), pre-existing hypertension (OR 1.59,95% CI 1.32, 1.91), and certain congenital anomalies. Also, smoking and increased maternal age were associated with birth weight discordance in both same-sex and opposite-sex twins.

CONCLUSIONS

Maternal hypertensive disorders, smoking and delayed childbearing were associated with intrapair birth weight discordance. The mechanisms of these associations deserve further investigation.

Mean arterial pressure in extremely low birth weight concordant and discordant twins during the first day of life

OBJECTIVE

To determine mean arterial pressure (MAP) values during the first 24 hours for stable concordant and discordant extremely low birth weight (ELBW) twins and to ascertain its association with perinatal factors.

BACKGROUND

In ELBW infants, whether singletons or concordant or discordant twins, hypotension is diagnosed by nonspecific clinical signs together with reference arterial pressure values extrapolated from regression models or from scarce actual observations.

DESIGN

Retrospective cohort study.

METHODS

We studied 26 sets of concordant and 29 sets of discordant twins, one of whom in each set weighed < or = 800 g at birth. Infants with umbilical cord hemoglobin > or = 14 g/dl and who, although mechanically ventilated, had normal acid-base balance, no patent ductus arteriosus, had not received indomethacin, steroids, muscle relaxants, narcotics, were never treated for hypotension, and survived at least 7 days were considered stable. Arterial pressures were determined by oscillometry (OBP) and direct transducer readings using an umbilical line (MAP). All admission and 10 % of the subsequent readings were measured by OBP; the remaining were measured by MAP.

RESULTS

Concordant and discordant twins were similar in demographics, history of chorioamnionitis, preeclampsia, antepartum steroids, cesarean delivery, and neonatal morbidity, but were different in mean birth weight (700 and 789 g), and gestational age (GA) (25 and 27 weeks). Forty-four (82%) of all concordant and 14 (26%) of 58 discordant twins were treated empirically for hypotension. Head ultrasounds were normal or showed Grade I/II in 74% concordant, 81% discordant, and 80% discordant infants with twin-to-twin transfusion syndrome (TTTX). Neonatal mortality was 46%, 45%, and 47%, respectively. There were 14 stable concordant and 22 stable discordant. Their MAPs were different at 1 hour (29 and 34 Torr), 3 hours (29 and 35 Torr), 6 hours (30 and 37 Torr), 12 hours (31 and 36 Torr), 18 hours (33 and 35 Torr), and 24 hours (34 and 36 Torr), respectively. Twenty-six small and 26 large concordant infants had similar MAP from the 1st (27 and 28 Torr) to the 24th hour of life (43 and 43 Torr). Concordant males (often not stable) had lower MAP than concordant females. Seventeen small discordant twins had lower MAP from 1 to 24 hours (28 and 33 Torr) than 17 large discordant twins without TTTX (32 and 38 Torr). Small discordant twins with (donors) and without TTTX had similar trends and MAP values. Large discordant twins with TTTX (recipient) had the highest MAP from birth to 24 hours than any other subgroup of infants and, unlike the others, the MAP trend decreased over time. MAP correlated with GA but not with very low birth weight (< or = 750 g), although with the same GA, those with higher birth weights had higher MAP, and at the same birth weight younger GA twins had lower MAP values.

CONCLUSION

MAP increases from birth to 24 hours in all concordant and discordant twins regardless of condition (stable or unstable), birth weight (large or small) or GA. Recipient TTTX twins had higher MAP throughout but, unlike the other twins, it declined over 24 hours. Small discordant and donor TTTX infants should be considered intrauterine growth restricted and are expected to have MAP commensurable to their GA and not to their birth weight.