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To relate unexplained antepartum fetal death with maternal and fetal characteristics in order to identify risk factors.Population-based study based on records of 1,676,160 singleton births with gestational ageor =28 weeks. Unexplained antepartum fetal death was defined as fetal death before labour without known fetal, placental, or maternal pathology.Although unexplained fetal mortality in general declined from 2.4 per 1000 births in 1967-1976 to 1.6 in 1977-1998, the proportion among all fetal deaths increased from 30% to 43% during the same period of observation. Unexplained fetal death occurred later in gestation than explained. From 39 weeks of gestation, the risk increased progressively to 50/10,000 in women agedor =35 years and10/10,000 in women25 years. In birth orderor =5, the risk was particularly high after 39 weeks of gestation. For birth weight percentile 2.5-9.9 andor =97.5, unexplained fetal death was four and three times more likely to occur, respectively. We found an additive effect of maternal age and birth weight percentile 2.5-9.9. Women with less than 10 years education had higher risk than women with 13 years or more (OR=1.6). Weaker associations were observed with female gender, unmarried mothers, and winter season.Unexplained antepartum fetal death occurred later in gestation than explained and was associated with high maternal age, multiparity, low education, and moderately low and high birth weight percentile. The increased risk in post-term pregnancies and the additive effect of maternal age and birth weight percentile 2.5-9.9 suggests that older women would benefit from monitoring of fetal growth.

To determine whether proportionate or disproportionate foetal smallness at 17 to 19 weeks of gestation in low-risk pregnancies was associated with size, body constitution, and adverse outcome at birth.We included ultrasound measurements at 17-19 weeks of gestation in 7285 uncomplicated pregnancies with reliable information on last menstrual period. We considered a foetus with both mean abdominal diameter (MAD) and biparietal diameter (BPD) below the 10th percentile for gestational age, gender, and parity as symmetrically small. Those who had MAD below the 10th percentile and BPD at or above the 10th percentile were asymmetrically small (thin and small).The occurrence of small for gestational age (SGA) (birth weight below the 10th percentile) decreased with increasing second trimester MAD percentile (P0.0001). The risk in foetuses which were both thin and extremely small (MAD below the 2.5th percentile) of having weight, ponderal index, crown-heel length, or head circumference below the 10th percentile at birth was 19-28%. The risk of perinatal composite outcome (prenatal death, Apgar score after 5 minor =7, birth weight below the 10th percentile, or1500 g, or preterm birth) was 37%. Apgar score ofor =7 at 5 min and explained foetal death both occurred in 7%, which was significantly higher than those with larger MAD.Asymmetric as well as symmetric foetal smallness may start early in pregnancy. Symmetric and particularly asymmetric small foetuses at 17-19 weeks of gestation were generally lighter, shorter, and thinner at birth and had more often adverse perinatal outcome.