The first trimester of pregnancy includes many changes that affect a woman’s body. A handful of these changes can also undermine sleep in pregnancy, and some develop soon after conception. It's possible for some of these to lead to symptoms characteristic of insomnia.
Women in the first 12 weeks of pregnancy commonly experience fatigue and excessive daytime sleepiness. More specifically, sleepiness affects up to 37.5% of pregnant women at 6 to 7 weeks, and is due to increasing levels of the hormone progesterone, which in turn leads to increased sleep fragmentation. Moreover, morning sickness, increased urinary frequency, back pain, breast tenderness, increased appetite, and anxiety can all disrupt sleep as well. It's a reasonable conclusion that these difficulties would disrupt a woman’s ability to stay asleep, resulting in insomnia.
By week 10 of pregnancy, women spend more time sleeping, with a longer sleep duration overnight, and frequent naps throughout the day. This is partly due to the fact that sleep has become more disturbed by frequent awakenings, and the amount of deep sleep decreases. Many pregnant women complain that their sleep is of poor quality during this period. Fortunately, it tends to improve in the second trimester, before sleep again worsens with the physical discomfort of late pregnancy.
Even though insomnia is a common occurrence during pregnancy, is it a reliable early indicator of pregnancy? The answer is probably "no": it may not occur often or early enough to be a useful sign. Moreover, insomnia is the most common sleep disorder in general, affecting millions of people of both sexes and all ages. Although it may be an early disruption of some pregnant women, it occurs so often in others that it's not a trustworthy sign specific to pregnancy.
If you have insomnia, no matter the reason, you should seek help to sleep better. And if you think you may be pregnant, you should simply take a pregnancy test and/or see your doctor to be certain.
Kryger, MH et al. "Principles and Practice of Sleep Medicine." ExpertConsult, 5th edition, 2011, pp. 1572-1576.