Hormones During the First Trimester of Pregnancy

Over the next nine months you’re in for a wild time! If pregnancy were an amusement park ride it might start off as the merry-go-round. By the second trimester you’re on the tilt-a-whirl, and by the third trimester you’re riding the big coaster! Fortunately, since pregnancy takes nine months, you’ll have some time to get used to all of the ups and downs. What exactly are these hormones doing inside your body?

Estrogen, progesterone, hCG, hPL, and prolactin are the major pregnancy hormones. Thyroid and adrenal hormones from both you and your baby also play roles. Let’s take a look at the five big players.


Estrogen is a female hormone produced in the ovaries. During your menstrual cycle, estrogen and progesterone levels cycle up and down, falling to their lowest levels while you are menstruating. Estrogen and progesterone stimulate the endometrium to support a fertilized egg if pregnancy occurs. During the first trimester, estrogen production is mostly made by the placenta, and this continues until near the end of the pregnancy when the amount circulating in your body is a thousand times the amount you have when not pregnant.

By improving the blood supply, estrogen makes everything grow. Breasts enlarge, moles and skin tags get bigger, spider veins become more prominent, and blood vessel beds become swollen and engorged.


Unlike estrogen, which is manufactured by the placenta, progesterone comes from the cholesterol connection in your own blood. Progesterone is a potent anti-inflammatory, which may help to blunt your immune system so you won’t reject your baby. It is also a smooth muscle relaxant, which can slow gastric emptying, giving you heartburn and acid reflux, and decreasing the tone of your bowels, leading to constipation. More bad news: it also increases the oiliness of your skin, so if you’re the fairest in all the land, you’ll be shocked to see that first zit in five years rear its ugly little head. Additionally, progesterone’s relaxant properties may play a role in keeping your uterus from contracting until term.

Together, estrogen and progesterone help control the onset of breast milk, keeping the floodgates closed by inhibiting the breasts’ response to the hormone prolactin. Estrogen and progesterone levels plunge at the time of delivery, allowing prolactin to stimulate the breasts’ milk flow.

Human Placental Lactogen (hPL)

Human placental lactogen is a growth hormone made by the placenta. It affects your metabolism by breaking down fat to provide nutrition for your developing baby.

Human Gonadotropic Hormone (hCG)

Except in the case of very rare ovarian tumors, hCG is produced only during pregnancy. Doctors can tell how well a pregnancy is progressing by measuring the increase in the amount of hCG. In a healthy pregnancy, hCG values double every two days or so in the early part of the first trimester.

The level of hCG plateaus near the end of the first trimester, leading doctors to believe it may have something to do with morning sickness (which usually lessens at this time). The most apparent biological effect of hCG is to regulate progesterone production from the site on your ovary where you ovulated, that part of the ovary remaining as something called the corpus luteum. This progesterone regulation plays a role in sexual differentiation of your baby.


Prolactin, the hormone that stimulates milk production, acts when the estrogen and progesterone decrease at the end of pregnancy. Thyroid hormones and insulin work together to pull this off, but prolactin is the main regulator for the onset and regulation of lactation.

While there isn’t much you can do to lessen the symptoms of surging hormones, understanding their role in your pregnancy just might help you tolerate the ride!

Article Posted 7 years Ago

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