Intended for healthcare professionals

Rapid response to:


Risk of recurrence of prolonged pregnancy

BMJ 2003; 326 doi: (Published 01 March 2003) Cite this as: BMJ 2003;326:476

Rapid Response:

Yes, natural gestation length has a strong genetic basis

It would be interesting to learn whether the shorter gestations
associated with a different father were also associated with a reduction
in the obstetric complications and perinatal morbidity typically
associated with prolonged pregnancy. I would expect not, because I think
the results of this study simply confirm that there are genetic influences
on normal, healthy gestation length, and that there is considerable
variation in the length of a normal, healthy pregnancy, depending on the

As someone who lives in an area where we have a great mixture of
genes from around the world, it seems obvious that the length of healthy,
normal gestation is affected by the genes of both mother and father. My
Asian clients tend to give birth before their due date, and I've seen some
hefty Asian newborns at 37 weeks gestation, with good dates. My
Mediterranean clients tend to give birth right around the due date. My
Caucasian clients tend to give birth on the later side, with most babies
coming 3-10 days after their due date. Germanic genes are notorious for
coming really, really late. I've seen Germanic babies born at 42 weeks
with a gestational age of 39 weeks - we hurried them along with aggressive
herbs to avoid the dreaded "postterm" situation. In cases where the mother
and father are from different genetic backgrounds, subsequent babies may
come at different times, depending on which parent they "take after".

And, in any case, add 5 days for a first baby and add another 5 days
for a boy baby.

All of this highlights the imprecise nature of setting a due date and
the tragedy of unnecessary inductions and consequent maternal and neonatal
morbidity for babies that are "postdates" but not truly postterm.
Similarly, it is possible for a baby to be postterm but not yet postdates,
thus being deprived of various types of surveillance beneficial to
postterm pregnancies.

Even the most precise dating of ovulation/conception/implantation
cannot predict the date of ideal fetal ripening without taking into
account the baby's genetics. Unfortunately, even complete knowledge of
the parents' genetics cannot predict the baby's genetic makeup, leaving
direct fetal genetic evaluation as the only certain way of determining
this, assuming that genetic analysis could find and interpret the correct
gene or genes. All of which leaves us back where we started, with an
Estimated Date of Delivery as a vague guideline, and term surveillance as
the best way of screening for problem postterm pregnancies.

Ambitious researchers could add much to the database of knowledge by
analyzing the natural length of normal, healthy pregnancies around the
world. However, this knowledge becomes less useful as human migration and
genetic blending increase.

Competing interests:  
None declared

Competing interests: No competing interests

28 February 2003
Veronica G. Falcao
Independent Licensed Midwife, California, USA
Mountain View, CA 94041 USA