Association of ultrasound estimated fetal weight between 10th and 50th centile in third trimester with the risk of spontaneous preterm delivery

Objective: To find out the association of ultrasound estimated fetal weight (UEFW) between 10th and 50th centile, in early third trimester and the risk of spontaneous preterm delivery. Materials and methods: Fetal weight of 965 women with singleton pregnancy was estimated between 28 and 34 weeks. Women with multiple gestation, medical disorders, fetal anomalies and induced labor were excluded. Values of UEFW were converted into centile values and multiples of median (MoM) for each gestational age. The risk of spontaneous preterm delivery was correlated with the UEFW. Results: Out of 965 subjects 62 were either excluded as per exclusion criteria or lost for follow-up. Out of 91 subjects with fetal weights ≤ 10th centile 17 (18.7%, OR 1.82, p-value 0.003) and out of 180 with that ≤ 20th centile 29 (16.1% OR 1.51, p-value 0.040) had preterm delivery. When the deviation was below 0.85 MoM, 15 out of 73 (20.5% OR 2.08, p-value 0.024) subjects had preterm delivery. Conclusion: When UEFW in early third trimester is below 20th centile or below 0.80 MoM the risk for spontaneous preterm delivery increases, hence, it may be prudent to be vigilant when the fetal weight is between 10th and 20th centile to avoid preterm delivery.