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Pregnancy hormones explained

Pregnancy Hormones FAQs

While a normal, healthy pregnancy can have a number of wonderful moments, women undergo a series of physical (both internal and external), emotional and psychological changes in their day to day life during pregnancy. And the majority of these changes are the consequence of hormonal release during the various stages of fetal development. Below you can find easy to reference questions to cover the various pregnancy hormones.

What is follicle stimulating hormone (FSH)?

This hormone exists regularly in your menstrual cycle. In the first days of your cycle, after the conclusion of your period, FSH stimulates one of your ovaries to begin the final part of the development of the egg-bearing follicles. Also, FSH stimulates this follicle to start producing oestrogen, which makes the endometrium (uterus´s inner layer) begin its rebuilding and, if you conceive, commands the shutting down of FSH secretion. This is why pregnant women do not ovulate.

What is lutenising hormone (LH)?

FSH begins the production of oestrogen, which triggers a blast of LH production. This process breaks the follicle and releases an egg (usually from the 12th to the 16th day in a 28 days cycle). The remaining portions of the follicle become the corpus luteum, which in a non-pregnant woman, disintegrates approximately in 14 days with the following beginning of the period.

If conception happens, the corpus luteum remains instead of disintegrating, keeps growing and producing enough hormones for the healthy development of the baby. This structure secretes progesterone, which allows the proper development of the uterus and, at the same time, inhibits LH production. The corpus luteum gradually shrinks near the 6 weeks of pregnancy and then, approximately at 12 weeks, the placenta continues doing this function.

What is human chorionic gonadotropin (hCG)?

You know about the little plus sign that appears in home pregnancy tests? That is the result of the presence of this hormone. This hormone is found in your urine and blood only during pregnancy and other related pathologies. Days after the fertilized egg implants in the endometrium, the newly developing placenta secrets hCG. This hormone stimulates the corpus luteum to liberate even more oestrogen and progesterone. Its levels can vary from woman to woman and from pregnancy to pregnancy. Your clinical physician may check its levels to monitor your pregnancy´s progress.

At the beginning of pregnancy, levels of hCG are very low, but then, these will double approximately every 48 hours until arriving at an increased peak between 7 and 12 weeks of pregnancy. Around the beginning of the second trimester, when the placenta takes over the production of oestrogen and progesterone, these levels start to decline. Despite this, hCG is present throughout pregnancy. This hormone has another job, suppressing your immune system to reduce the chances of your body rejecting the baby.

What is oestrogen?

This hormone, beside progesterone, is one of the most important ones. oestrogen that comes from the ovaries, the corpus luteum and then from the placenta, makes the uterus grow, develops endometrium, increases blood flow especially in this region and regulates the liberation of other important hormones. oestrogen increases the growth of your breasts and their milk-making machinery. It also makes sure of the development of the organs and systems of your baby.

Oestrogen is responsible for the increase of blood flow to mucous membranes producing stuffy nose, sinus congestion, postnasal drip and headaches. Dermatologically speaking, this increased blood flow results in the famous pregnant “glow”. Along with progesterone, can cause hyperpigmentation such as darkening of the areola-nipple complex and the middle white line in your abdomen (linea alba). The skin of your face may start to look more tanned, producing the chloasma or “mask of pregnancy”, due to the more sensitivity that your skin feels to sunlight.

What is progesterone?

This is the other mother of pregnancy hormones. Produced by the same structures like the ones that produce oestrogen, it has similar functions such as the placenta and endometrium maintenance, and breasts growth. It also makes sure of the smooth muscle of the uterus expansion for your baby to grow healthy. However, this process produces many gastrointestinal discomforts. Progesterone helps to soften cartilage, loosening joints and ligaments, preparing for labour. Produces gums swelling and bleeding, and acne.

What is human placental lactogen?

Also known as human chorionic somatomammotropin, also prepares your breasts for lactation. Allows the secretion of colostrum, the rich in nutrients pre-milk that your breasts secrete before true milk. It changes maternal metabolism so that pregnant women consume more fatty acids and less glucose so that the growing baby has more energy available for development.

What is relaxin?

This hormone helps relax your body´s muscles, joints and ligaments, preparing them for labour. Smooth muscle in the uterus and cervix and the sacrococcygeal joint especially benefits from this during delivery. These relaxed structures can make your balance a little unsteady, so be careful when you walk.

What is oxytocin?

This is the pregnancy´s muscle-contracting hormone and is present during all pregnancy, but your uterus becomes more sensitive to it as this go on. When your baby is ready to born, oxytocin produces uterine contractions. Immediately after delivery, oxytocin is used for your womb shrinking. Then, while your baby is sucking your milk, oxytocin is also released for further uterus involution and for the contraction of your mammary gland cells to secrete milk.

What is prolactin?

Also known as luteotropic hormone, is the principal hormone in charge of milk production by stimulating mammary glands. It plays a major role in maternal behaviour. It also has a stimulating effect on the adrenal glands which can lead to excessive hair growth anywhere in your body. Do not worry, the extra hair will eventually disappear months after delivery.

What is placental growth factor?

This hormone promotes blood vessel growth to assure a healthy blood flow from the placenta to your baby. Low levels of this hormone have been associated with pre-eclampsia (high blood pressure during pregnancy).


Nuchal Translucency

12-14 weeks


Anatomy Survey

21-22 weeks


Later Dating

10-17 weeks


Gender Scan

19 weeks onwards


Growth & Well Being

22 weeks onwards


Post Dates & Liquor

40 weeks onwards


What Our Patients Say

Gráinne Macken

This is my second visit to Merrion Fetal, I was very pleased on both occasions. Lovely quiet waiting room, appointment was on time. The 20-week scan is very detailed we enjoyed watching our baby on the large TV screen. We got some beautiful photos. The nurse was very pleasant and talked us through all the measurements and anatomy. I would highly recommend this scanning clinic.”

Áine Gibney

I had the best experience at the Merrion Fetal Health clinic for my 20-week big scan. The staff were so friendly and so nice and the lovely lady who did my ultrasound scan was amazing. She was so thoroughgoing to absolutely everything and gave me such reassurance on how my baby was growing and developing. I would recommend any Mother to be to attend here if you are looking for a comfortable, reassuring and super pleasant experience.”

Linda O'Sullivan

Highly recommend! We had an early scan due to a little scare at the start of pregnancy and then another at 12 weeks to make sure all was good again. Helen who was scanning on both days was fantastic. We felt totally relaxed and un-rushed while she took her time finding the best angle of baby to get us the clearest pictures as keepsakes all while making sure everything was perfect with baby. She reassured us throughout and I can honestly say it was the best money we ever spent getting both scans done.

Please let Helen know we are 18 weeks now and flying along Highly recommend!



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All articles on the blog and website are intended as information only. Please do not consider any of the information provided here as a substitute for medical advice. At all times seek medical advice directly with your own doctor and medical team.


This website was formerly Merrion Fetal Health. The clinic has undergone a rebrand and is now known as Merrion Ultrasound.