The risk of preterm delivery ( < 37 weeks of gestation) is approximately nine times higher in women with multifetal pregnancies than in women with singleton pregnancies. However, it is possible that the risk will vary according to gestational week. To assess the risk of premature birth within 1 week by gestational age among multifetal pregnancies and compare the estimated risk with that of singleton pregnancies, we analyzed 6 036 475 infants born in singleton pregnancies and 90 887 infants born in multifetal pregnancies in Japan ( ≥ 22 weeks) over the 5-year period 1989–1993. An estimate of the risk of birth within 1 week at gestational week n was obtained by dividing the number of infants delivered at gestational week n by the number of infants delivered at or beyond gestational week n. The risk at 22 weeks was 0.9 per 1000 fetuses for singleton pregnancies and 5.0 per 1000 for multifetal pregnancies. The risk remained relatively stable until 27 weeks of gestation, then sharply increased toward 36 weeks of gestation in both singleton and multifetal pregnancies. The odds ratio for birth within 1 week for fetuses of multifetal pregnancies compared with fetuses of singleton pregnancies was 5.9 (95% CI, 5.4–6.5) at 22 weeks of gestation, increasing gradually with increasing gestational age until 33 weeks of gestation (13.7; 95% CI, 13.1–14.2) but declining thereafter to 8.8 (95% CI, 8.6–8.9) at 36 weeks of gestation. Results of data analysis for each year of the 5-year period did not differ substantially. Twin Research (2000) 3, 2–6.

This study evaluated carnitine and lipid status of fifty Korean newborns. Each subject was assigned to two groups: one according to body weight at birth and the other according to gestational age. Serum total, HDL- and LDL-cholesterol were significantly lower and triacylglycerols were significantly higher, by 14 %, in the low birth weight infant (LBWI, 1310–2490 g) group compared with the normal birth weight infant (NBWI, 2570–4420 g) group. Neither birth weight nor gestational age affected serum total carnitine concentrations. However, serum ASAC (acid-soluble acylcarnitine) concentrations were 43 % higher (P < 0·001) in the LBWI group compared with the NBWI group, and approximately twice as high (P < 0·05) in the 28–32 gestational age group compared with the other gestational age groups. NEC (non-esterified acyl carnitine) fractions were significantly higher in the NBWI and 28–32 week groups (P < 0·001 and P < 0·05); consequently serum acyl/NEC carnitine ratios were four times higher in the LBWI group compared with the NBWI group and 2–3 times higher in the 25–32 week age group compared with the more advanced gestational age groups. Urinary carnitine excretion, including the NEC fraction and total carnitine, was significantly higher (P < 0·001) for LBWI than for NBWI. By gestational age, NEC excretion of the 28–32 week group was significantly (P < 0·05) higher than that of the other two groups, but total carnitine excretion was not different among the groups. This study demonstrated that Korean immature and preterm newborns have higher serum triacylglycerol concentrations but lower carnitine status than NBWI. Therefore, the lower carnitine status and moderately higher triacylglycerols may suggest that LBWI in Korea might be at risk for poor carnitine status and decreased capacity to utilise fatty acids for energy.