Is Cesarean Delivery Preferable in Twin Pregnancies at >=36 Weeks Gestation?

BACKGROUND: The optimal mode of delivery in twin pregnancies remains controversial. A recent randomized trial did not find any benefit of planned cesarean vs. vaginal delivery at 32-38 weeks gestation, but the trial was not powered to detect a moderate effect. We aimed to evaluate the impact of cesarean delivery on perinatal mortality and severe neonatal morbidity in twin pregnancies at ≥32 weeks through a large database exploration approach with the power to detect moderate risk differences. METHODS: In a retrospective birth cohort study using the U.S. matched multiple births, 1995-2000 (the available largest multiple birth dataset), we compared perinatal outcomes in twins (n = 181,810 pregnancies) delivered at 32-41 weeks gestation without congenital anomalies. The primary outcome was a composite of perinatal death and severe neonatal morbidity. Cox regression was used to estimate the adjusted hazard ratio (aHR) controlling for the propensity to cesarean delivery, fetal characteristics (sex, birth weight, birth weight discordance, same-sex twin or not) and twin-cluster level dependence. Prospective risks were calculated using the fetuses-at-risk denominators. RESULTS: The overall rates of the primary outcome were slightly lower in intended cesarean (6.20%) vs. vaginal (6.45%) deliveries. The aHRs of the primary outcome were in favor of vaginal delivery at 32 (aHR = 1.06, p = 0.03) or 33 (aHR = 1.22, p<0.001) weeks, neutral at 34-35 weeks, but in favor of cesarean delivery at 36 (aHR = 0.94, p = 0.004), 37, 38 and 39+ weeks (aHR: 0.72 to 0.78, all p<0.001). The lower risk of the primary outcome for cesarean vs. vaginal deliveries at 36+ weeks of gestation remained when the analyses were restricted to different-sex (dichorionic) twins (aHR = 0.84, 95% CI 0.80-0.88). CONCLUSION: Cesarean delivery may be beneficial for perinatal outcomes overall in twin pregnancies at ≥36 weeks gestation.

Haplotype-based approach for noninvasive prenatal tests of Duchenne muscular dystrophy using cell-free fetal DNA in maternal plasma.

PURPOSE: This study demonstrates noninvasive prenatal testing (NIPT) for Duchenne muscular dystrophy (DMD) using a newly developed haplotype-based approach. METHODS: Eight families at risk for DMD were recruited for this study. Parental haplotypes were constructed using target-region sequencing data from the parents and the probands. Fetal haplotypes were constructed using a hidden Markov model through maternal plasma DNA sequencing. The presence of haplotypes linked to the maternal mutant alleles in males indicated affected fetuses. This method was further validated by comparing the inferred single-nucleotide polymorphism (SNP) genotypes to the direct sequencing results of fetal genomic DNA. Prenatal diagnosis was confirmed with amniocentesis, and those results were interpreted in a blinded fashion. RESULTS: The results showed an average accuracy of 99.98% for the total inferred maternal SNPs. With a mean depth of 30× achieved in the 10-Mb target region of each sample, the noninvasive results were consistent with those of the invasive procedure. CONCLUSION: This is the first report of NIPT for DMD and the first application of a haplotype-based approach in NIPT for X-linked diseases. With further improvements in accuracy, this haplotype-based strategy could be feasible for NIPT for DMD and even other X-linked single-gene disorders.

Diabetes and perinatal mortality in twin pregnancies.

BACKGROUND: Diabetes in pregnancy has been associated with a paradoxically reduced risk of neonatal death in twin pregnancies. Risk "shift" may be a concern in that the reduction in neonatal deaths may be due to an increase in fetal deaths (stillbirths). This study aimed to clarify the impact of diabetes on the risk of perinatal death (neonatal death plus stillbirth) in twin pregnancies. METHODS: This was a retrospective cohort study of twin births using the largest available dataset on twin births (the U.S. matched multiple birth data 1995-2000; 19,676 neonates from diabetic pregnancies, 541,481 from non-diabetic pregnancies). Cox proportional hazard models were applied to estimate the adjusted hazard ratios (aHR) of perinatal death accounting for twin cluster-level dependence. RESULTS: Comparing diabetic versus non-diabetic twin pregnancies, overall perinatal mortality rate was counterintuitively lower [2.1% versus 3.3%, aHR 0.70 (95% confidence intervals 0.63-0.78)]. Individually, both stillbirth and neonatal mortality rates were lower in diabetic pregnancies, but we identified significant differences by gestational age and birth weight. Diabetes was associated with a survival benefit in pregnancies completed before 32 weeks [aHR 0.55 (0.48-0.63)] or with birth weight <1500 g [aHR 0.61 (0.53-0.69)]. In contrast, diabetes was associated with an elevated risk of perinatal death in pregnancies delivered between 32 and 36 weeks [aHR 1.38 (1.10-1.72)] or with birth weight >=2500 g [aHR 2.20 (1.55-3.13)]. CONCLUSIONS: Diabetes in pregnancy appears to be "protective" against perinatal death in twin pregnancies ending in very preterm or very low birth weight births. Prospective studies are required to clarify whether these patterns of risk are real, or they are artifacts of unmeasured confounders. Additional data correlating these outcomes with the types of diabetes in pregnancy are also needed to distinguish the effects of pre-gestational vs. gestational diabetes.

[A pilot study on spinal muscular atrophy carrier screening in Shanghai region using real-time PCR].

OBJECTIVE: To develop a screening program for spinal muscular atrophy (SMA) carriers, and to assess the carrier frequency and detection rate in Shanghai region. METHODS: Quantitative analysis of the SMN1 gene by real-time PCR was developed using specimens from 15 SMA patients and 76 SMA parents from 38 affected nuclear families. A pilot screening was carried out for 1741 asymptomatic pregnant women. Frequencies of SMN1 alleles were determined with the Hardy-Weinberg equilibrium. RESULTS: Forty five out of the 1741 women were identified as SMA carriers by the presence of single copy of SMN1. The frequencies of no copy, 1 copy, 2 copy and 3 copy alleles were 1.37 U+00D7 10-2, 9.45 U+00D7 10-1, 2.80 U+00D7 10-2 and 1.27 U+00D7 10-2, respectively. The adjusted SMA carrier frequency was 1:35 with a detection rate of 94.49%. For those with a negative screening result, individuals with 3 copies carried a higher residual risk. CONCLUSION: The incidence of SMA carriers in Shanghai region is similar with that in Caucasian populations. Carrier screening has high detection efficiency. An effort should be made to further distinguish SMN1 gene copy numbers for those with more than 2 copies, since accurate determination of 2 and 3 copy allele frequencies is essential for post-screening genetic consulting.