The average single baby grows about 35 grams (1.2 ounce) per
week during the first trimester and grows increasingly faster to reach a
maximum growth rate of almost 250 grams (8.8 ounces) per week by 33
weeks . Growth then slows down and is about 75 grams (2.7
ounces) per week by 40 weeks. At term the average single baby weighs
about 3400 grams 7 1/2 pounds .
Twins usually grow at the same rate as single babies
until about 30 to 32 weeks' .The growth rate of twins peaks at 31
weeks 175 grams (6 ounces ) per week and gradually slows down to about 2 ounces
per week by 40 weeks. The average fraternal twin weighs 5 pounds 8 ounces at
birth. Identical twins weigh less at 4 pounds 12 ounces .
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REFERENCES Resnik R .Intrauterine growth restriction.
Obstet Gynecol. 2002 Mar;99(3):490-6. PMID: 11864679
Williams RL, et. al., Fetal growth and perinatal
viability in California.
Obstet Gynecol. 1982 May;59(5):624-32.