Objectives: To estimate the risk of second-trimester miscarriage in women with low risk of carrying a fetus with chromosomal abnormality, according to nuchal translucency (NT) screening, and to determine whether NT thickness or other factors affect the risk.
Methods: The study population comprised 14 278 singleton pregnancies with a risk of Down syndrome < 1:250 at NT scan, and where no fetal karyotyping was performed < 25 weeks. Risk factors for miscarriage were investigated by logistic regression.
Results: The median risk of Down syndrome was 1 : 3138 (range 1 : 9651-1 : 251) and median NT was 1.7 (range 0.4-3.0) mm. The miscarriage rate was 0.5% (77/14 278; 95% CI 0.4-0.6). After having controlled for maternal age, we found the number of previous deliveries and miscarriages to independently predict miscarriage: odds ratio (OR) for each previous delivery 1.48, 95% CI 1.22-1.94, 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).
Conclusion: In singleton pregnancies with 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.
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