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Oral communication abstracts odds ratio (OR) for each previous delivery 1.48 (95% CI, 1.22-1.80), P < 0.0001; OR for each previous miscarriage 1.34 (95% CI, 1.07-1.68), P = 0.01. Excluding women with any previous miscarriage and adjusting for parity we found a U-shaped relationship between maternal age and miscarriage (P = 0.04). Conclusions: In singleton pregnancies with an estimated risk of Down syndrome < 1 : 250 according to NT screening at 12-14 weeks, the spontaneous fetal loss rate before 25 weeks is likely to be around 0.5%. NT thickness up to 3 mm does not seem to affect the risk of miscarriage in such pregnancies. Instead, the risk seems to increase with number of previous miscarriages and deliveries, and possibly the risk is highest in the youngest and oldest women. OC57 Enlarged nuchal translucency in the same woman in different pregnancies

Background: Duchenne muscular dystrophy (DMD) has showed a wide spectrum of mutations in the dystrophin gene including exon deletions, duplications and small mutations. This retrospective study was to supply information of the DMD mutational spectrum in 303 Chinese families and further offer 5-year clinical experience of DMD genetic counselling and prenatal diagnosis.Methods: In this retrospective study, 305 pregnancies in 303 pregnant women who has a birth history of DMD patients underwent prenatal diagnosis using multiplex ligation-dependent probe amplification (MLPA) followed by Sanger sequencing between 2014 and 2018. Karyotype analysis was performed to exclude fetal abnormal karyotype.Results: The detection rate of DMD gene mutation in 303 probands was 97.7% with 7 families having a negative genetic diagnosis. The mutational spectrum comprised of large arrangements in 288/303 (95.0%) and small mutations in 8/303 (2.6%). 204 pregnant women did carrier testing among whom, 108 mothers had the same mutation as family proband. Of the 305 pregnancies underwent prenatal diagnosis, 55 of 173 male fetuses were affected. We also performed karyotype analysis and found 3 abnormal karyotypes of trisomy 21. We even found a fetus with DMD gene mutation and trisomy 21 in a same fetus by further analysis.Conclusions: The distribution and mutation profile of 303 probands and 305 fetuses were demonstrated. Given the large samples provided in this study, the information is essential for genetic counselling and prenatal diagnosis in DMD families in China.