The female reproductive hormones known as oestrogen and progesterone play a role not only in regulating a female’s menstrual cycle but also in upholding a pregnancy. During pregnancy, a female’s reproductive hormones undergo changes along with other hormones in order to supply the necessary needs and growth for the foetus. Not only do endocrine hormones change, but so do some of the metabolic processes. There are also hormones produced by the placenta to ensure the growth and health of the foetus.
Hormonal Changes
Progesterone
Progesterone is a hormone that is in a symbiotic relationship with oestrogen. Along with oestrogen, it regulates a female’s menstrual cycle. When a female undergoes her menstrual cycle, progesterone is the hormone that peaks in the second part of the menstrual cycle. Progesterone plays a vital role during pregnancy as it is this hormone that prepares the endometrium, or the lining of the uterus, for implantation of a fertilised egg and also creates a favourable environment for a pregnancy to take place. This hormone plays an important role in maintaining a pregnancy.
Progesterone levels tend to rise during the first 8–10 weeks after conception. These progesterone levels are mostly produced by the female’s corpus luteum. It is a structure that forms in the ovaries which releases progesterone until week 10 of gestation. It usually disappears if fertilisation does not take place. After 10 weeks, the foetal placenta becomes competent in producing its own progesterone, especially between 10 and 12 weeks, where it produces about 250mg/day.
As the placenta starts to produce its own progesterone, the corpus luteum’s levels start to return to baseline at about week 10 after gestation. Interestingly, the high levels of progesterone also play a protective role by suppressing the mother’s immune response to the foetus’ antigens.
Oestrogen
Oestrogen levels tend to rise gradually during pregnancy. Unlike progesterone, oestrogen is not made directly by the placenta. Except for the maternal elevated levels of oestrogen, oestrogen levels can rise due to the pregnancy.
Oestrogen crosses the placenta from the foetus’ side. This happens due to the fact that most cells that make up the placenta do not contain the necessary enzymes to directly produce oestrogen. Instead, a certain hormone from the adrenal gland of the foetus is used as a precursor to form oestrogen in the placenta, which can then move over to the mother’s side, resulting in an increased amount of oestrogen. Oestrogen levels differ during different trimesters.
Human Chorionic Gonadotropin (hCG)
hCG is a hormone that forms part of the cells in the placenta. This hormone’s levels only start to arise during pregnancy and is also the hormone that is tested for in a blood or urine sample to diagnose a pregnancy. Studies have shown that hCG can be found in blood samples as early as 11 days after conception. hCG is also known for its main role in supporting the corpus luteum in the production of progesterone during the first 10 weeks of gestation, taking over for luteinising hormone (LH) from the pituitary gland.
Human Placental Lactogen (hPL)
This hormone is produced in the placenta and starts to rise as levels of hCG start to decline around the period of 10–12 weeks of gestation. hPL levels are in a direct relationship with placental growth, meaning that hPL levels rise as the placenta grows. It is also an indicator of placental health. This hormone tends to work in maternal tissue and is also thought to increase the mother’s insulin-like growth factor type 1 (IGF-1) concentrations during pregnancy. This hormone can lead to insulin resistance, inhibit the production of glucagon from the pancreas, and can lead to gestational diabetes. It is thus important to test blood glucose levels during the course of the pregnancy, especially in the last trimester as it is then when hPL levels are at their highest.
Calcium Concentrations
The calcium levels of the foetus are regulated by maternal calcium levels that travel across the placenta. Maternal calcium levels change in order to maintain foetal bone growth and it is thus recommended that mothers increase their dietary intake of calcium and vitamin D as vitamin D helps to increase the absorption of calcium in the body. As calcium concentrations fluctuate during pregnancy, so would the parathyroid hormone along with calcitonin, as it helps to regulate calcium levels in the body.
Thyroid Hormones
Studies have shown that a change in thyroid hormones, be it hyperthyroidism or hypothyroidism, can have severe effects on maternal and foetal health if left untreated. There are certain therapy regimes that are indicated to treat these conditions during pregnancy.
