Perinatal mortality in the East Flanders Prospective Twin Survey (preliminary results)

Cortisol advantage of neighbouring the opposite sex in utero

Population sex ratios naturally fluctuate around equality. It is argued that the production of an equal number of male and female offspring by individual parents should be favoured by selection, if all costs and benefits are equal. Theoretically, an even sex ratio should yield the highest probability for a fetus to be adjacent to a fetus of the opposite sex in utero. This may cause developmental costs or benefits that have been overlooked. We examined the physiological and developmental parameters associated with in utero sex ratios in the nutria (Myocastor coypus), an invasive wildlife species with a strong reproductive output. Using hair testing, we found that litters with even sex ratios had the highest average cortisol levels. Fetuses neighbouring the opposite sex exhibited longer trunks than those neighbouring the same sex, which might imply better lung development. Our results are the first, to our knowledge, to link intra-utero sex ratios and fetal cortisol and suggest that fetal cortisol might be a mechanism by which even sex ratios are maintained via developmental advantages.

The East Flanders Prospective Twin Survey (Belgium): a population-based registe

The East Flanders Prospective Twin Survey (EFPTS), started in 1964, is unique among the 17 major European twin registers because it is population based, the twins (and higher order births) are ascertained at birth, basic perinatal data are collected, chorion type is established and, when appropriate, genetic markers including DNA fingerprints, are determined. The total number of sets is 5089 twin, 158 triplet and 14 of higher order. Zygosity has been diagnosed on the basis of sex, placental structure and genetic markers in more than 95% of pairs. The EFPTS is the only large register that includes placental data and allows differentiation of three subtypes of monozygotic twins based on the time of the initial zygotic division: the dichorionic—diamnionic pairs (early), the monochorionic—diamnionic pairs (intermediate), and the monochorionic—monoamnionic pairs (late). Methodology and basic results in twins are considered in this article; detailed studies will be reported later. The sex proportion in dizygotic (DZ) twins is the same as in singletons, whereas monozygotic (MZ) twins number more girls than boys. The difference in perinatal mortality between DZ and MZ twins is limited to the monochorionic MZ subgroup. Birth weight is highest in DZ twins and diminishes stepwise in MZ dichorionic and MZ monochorionic twins. Duration of pregnancy follows the same trend but is limited to a few days. Iatrogenic pregnancies are increasing to the point of representing almost 50% of the twin births in 1997.

Intrauterine growth in multiple pregnancies in relation to fetal number, chorionicity and gestational age

OBJECTIVES

To examine birth weight in dichorionic and monochorionic twins and trichorionic triplets, and to estimate the relative independent importance on growth of fetal number, chorionicity and gestational age.

METHODS

Four groups of pregnancies were examined: 12,816 singleton pregnancies, 302 monochorionic twin pregnancies, 569 dichorionic twin pregnancies, and 97 trichorionic triplet pregnancies. Chorionicity was determined at 10-14 weeks on the basis of the presence or absence of the lambda sign in twins, and by examining the ipsilon zone in triplets. The relationship between birth weight and gestational age in singletons was established, and using this equation the expected mean birth weights for all gestational ages were calculated. For each case in all groups, the difference between the observed birth weight for each fetus and the appropriate normal mean for gestation in singletons was calculated (Z-score). Multiple regression analysis was used to examine the independent contribution of gestational age, number of fetuses and chorionicity in the prediction of actual birth weight and birth weight Z-score.

RESULTS

Birth weight Z-score was significantly lower than the expected mean in singletons for dichorionic twins, monochorionic twins and trichorionic triplets (t = 15.4, P < 0.0001, t = 21.7, P < 0.0001 and t = 19.9, P < 0.0001, respectively). Furthermore, the reduction in expected birth weight was significantly greater for monochorionic twins and trichorionic triplets compared with dichorionic twins (t = 6.3, P < 0.0001 and t = 7.8, P < 0.0001, respectively). Multiple regression analysis demonstrated that number of fetuses, presence of a monochorionic placenta and gestational age were independently associated with birth weight Z-score, the strongest effect being fetal number, followed by monochorionicity (t = - 23.4, P < 0.0001, t = - 8.3, P < 0.0001 and t = - 4.9, P < 0.0001, respectively).

CONCLUSIONS

The finding that monochorionic twins were of lower adjusted birth weight than dichorionic twins, and the significant independent effect of chorionicity on birth weight suggest that monochorionic placentation in itself has an effect on intrauterine growth. The effect of fetal number independent of chorionicity is demonstrated by the lower birth weight of trichorionic triplets compared with dichorionic twins.

Birthweight and perinatal mortality among singletons and twins in north-eastern Tanzania

BACKGROUND

Low birthweights as well as high perinatal mortality rates are common in most African populations. Little is known, however, about how low birthweight corresponds with higher mortality rates within African populations. Twins are known to have lower birthweights and higher perinatal mortality rates than singletons. If lower birthweights represent higher perinatal risk per se, small twins within a population with generally lower birthweights should have critically increased risks.

METHODS

In total, 15,255 births in a Tanzanian hospital during 1999-2006 were analysed to determine birthweight distribution and examine perinatal mortality rates (including stillbirths and neonatal deaths within 24 hours) by birthweight in twins and singletons. Referral births from outside the district where the hospital was situated were excluded from analysis.

RESULTS

The mean birthweight for births within an estimated normal distribution was 3,172 g, with a standard deviation of 462 g. The overall perinatal mortality rate was 43.9 per 1,000 births (95% confidence interval: 40.7-47.2). Perinatal mortality rates among twins and singletons were 91.0 and 41.1 per 1000 babies respectively, corresponding to a relative risk of 2.2 (95% confidence interval: 1.7-2.8). The birthweight distribution for twins was shifted to lower birthweights. Twins had a generally lower birthweight and an excess of extremely small births as compared to singletons. The increased mortality rate for twins appeared to be independent of birthweight.

CONCLUSIONS

The two-fold increased risk of perinatal death for twins was observed across the whole birthweight distribution, and very small twins appeared to have an excess perinatal risk that was almost similar to that of larger twins.

Second-trimester amniocentesis vs. chorionic villus sampling for prenatal diagnosis in multiple gestations

OBJECTIVE

To study the impact of invasive procedures for prenatal diagnosis on multiple pregnancies and compare first-trimester chorionic villus sampling with second-trimester amniocentesis.

DESIGN

Retrospective study of 347 second-trimester amniocenteses and 69 chorionic villus sampling procedures.

RESULTS

Miscarriage occurred in 4.18% of women after amniocentesis and 4.54% of women after chorionic villus sampling. In the amniocentesis group the risk of miscarriage was higher in the cases with transplacental entry (4.54%) than in those with transamniotic entry (2.08%). The rates of preterm delivery < or = 32 weeks and preterm delivery < or = 35 weeks in the amniocentesis group were 11.8% and 32.4% and in the chorionic villus sampling group 16.66% and 23.8%, respectively. Total fetal loss rate was similar in the amniocentesis group (8.8%) and the chorionic villus sampling group (10.22%). In the 21 cases where selective feticide was carried out the total fetal loss rate was lower in the chorionic villus sampling group (8.3%) than in the amniocentesis group (11.1%), although the difference did not reach statistical significance.

CONCLUSION

Chorionic villus sampling appears to be a safe alternative to amniocentesis and should be considered as the method of choice particularly when there is a high risk of an affected fetus necessitating selective feticide.

Management of single fetal death in twin-to-twin transfusion syndrome: a role for fetal blood sampling

OBJECTIVE

Intrauterine death of one twin in monochorionic pregnancies is associated with an increased mortality and morbidity of the cotwin. This is likely to occur as a consequence of acute hemodynamic changes due to feto-fetal hemorrhage at the time of death of the cotwin. We assessed the role of fetal blood sampling and intrauterine transfusion to rescue the survivor.

MATERIALS AND METHODS

We managed 12 cases of single intrauterine death at between 17 and 26 weeks' gestation in monochorionic twins complicated by twin-to-twin transfusion syndrome (TTTS). All these cases had been treated either by laser therapy or by serial amniodrainage. When the demise of one twin occurred, ultrasound-guided fetal blood sampling was performed in the surviving twin using a 20-gauge needle within 24 h of death. Intrauterine transfusion was performed at the same time in cases where the survivor was anemic. All survivors were assessed in the neonatal period and at 1 year of age.

RESULTS

Six of the 12 surviving fetuses were found to be anemic and underwent intrauterine transfusion. All fetuses survived the procedure. Four of these fetuses had normal neurological development at 1 year of age. Periventricular leukomalacia developed in one case and the patient underwent termination of pregnancy at 34 weeks. In one case delivery occurred at 34 weeks' gestation and the baby developed periventricular leukomalacia at 1 month of age. In all six non-anemic fetuses pediatric examination was normal at birth and at 1 year of age.

CONCLUSION

Intrauterine death of one monochorionic twin in TTTS puts the survivor at high risk of intrauterine death or of developing ischemic/hypoxic lesions. Our results suggest that fetal blood sampling is a useful diagnostic tool to identify those fetuses that are not anemic and hence unlikely to be at risk of developing a cerebral lesion.

Why do small twins have a lower mortality rate than small singletons?

OBJECTIVE

We propose an interpretation of the paradoxically better survival rate among low-birth-weight twins compared with low-birth-weight singletons.

STUDY DESIGN

We used data from Belgian birth and death certificates for 1983 and 1984. The data include 229,964 singletons, 2175 first twins, and 2153 second twins. Weight-specific perinatal mortality rates of twins and singletons were compared; the birth-weight distributions were adjusted to a single mean and SD.

RESULTS

After adjustment, mortality rates at every weight were higher for twins than for singletons.

CONCLUSIONS

The appearance of better survival among small twins compared with small singletons disappears after adjustment to relative birth-weight. There is a large risk resulting from twinning that falls on all twins, regardless of their weight.