Spontaneous fetal loss rates in a non‐selected population

The objective of this work was to determine the rate of spontaneous fetal loss up to 28 weeks of gestation in uncomplicated pregnancies of a low‐risk population after sonographically identified intact intrauterine pregnancy during the first trimester. Transvaginal ultrasounds were given to 2,534 women at between six and 12 weeks of gestation. Inclusion criteria were a positive fetal cardiac activity and no antecedent signs of vaginal bleeding. Gestational age was confirmed by measurement of the crown‐rump length and/or biparietal diameter (BIP). Patients were followed until delivery or up to a fetal loss. The mean fetal loss rate between 12 and 28 weeks was 3.86% (n = 99). Fetal loss increased with maternal age: fetal loss rate under 20 yr: 2.94% (OR 0.75; CI 0.23–2. 46), 20–24 yr: 3.20% (OR 0.77; CI 0.48–1.23), 25–29 yr: 3.39% (OR 0.77; CI 0.50–1.19), 30–34 yr: 3.89% (OR 1.01; CI 0.59–1.71), 35–39 yr: 7.82% (OR 2.13; CI 1.04–4.32), 40–45 y: 50% (OR 13.84; CI 6.67–28.72) and > 45 yr: 50% (OR 13.05; CI 1.96–86.71) respectively. The frequency of spontaneous fetal loss before 28 weeks gestation was assessed systematically in a low‐risk population. There was a very clear correlation with advancing maternal age. These data now can be used as background loss rate information for evaluating the safety of invasive prenatal diagnosis, and they will be more valid for this purpose than the available data taken from selected cohorts of women, such as those from hospital clinics or from infertility programs. © 2001 Wiley‐Liss, Inc.