Hormonal changes during
pregnancy, when the sex hormone levels show profound fluctuations, are the key
factor that will determine whether or not your migraine get better or worse. When
successful egg fertilization occurs, the fertilized egg is implanted in the
uterus and a variety of hormones are produced, including human chorionic
gonadotropin, or hCG, the substance that is measured by pregnancy tests. Although
the ovaries continue to produce estrogen early on, as pregnancy develops the
placenta begins to produce estrogen as well. As the pregnancy progresses,
estrogen, progesterone, and hCG levels increase significantly.

Estrogen levels rise dramatically during pregnancy and drop
precipitously after delivery. Compared to first-trimester levels, estrogen
increases by six folds by the third trimester and then drops to almost
undetectable levels after delivery. However, the fluctuation of levels is not
as pronounced as during the non-pregnant state, which may be why migraine often
improves during pregnancy. This improvement may also be due to the increased
levels of natural pain-killing hormones (endorphins). These are several times
higher during pregnancy, and though the relief from migraines they provide
might last the whole pregnancy, the levels settle back down after delivery,
normally allowing migraine attacks to recur.

Many women report that their migraine headaches improve as
estrogen levels surge during pregnancy. Improvement usually begins at the end
of the first trimester. This trend usually persists throughout the remainder of
pregnancy, while estrogen levels remain elevated. Upon delivery, estrogen
levels drop sharply, so the protection estrogen confers against headache is
lost. As a result, migraine attacks ensue.

However, it is not always the case that your migraine will
improve, especially in the early weeks of pregnancy. For some women, migraine
can go on unchanged, or more rarely even get worse.

So in a nutshell: even if headaches improve during
pregnancy, they typically return during the first 1—4 weeks after delivery. As
already noted, estrogen and progesterone levels remain high during the third
trimester. Delivery of the placenta after the baby is born is accompanied by a
sudden drop in progesterone and estrogen. Estrogen levels will remain low for
the next several months. Remember that the fall in progesterone helps to
stimulate the production of breast milk.

In most cases, headaches return to the pre-pregnancy pattern
after delivery. If you choose to breastfeed, you’re less likely to have your
headache return during the first month after your baby is born.