Every organ in the body shifts during pregnancy, and muscles and joints move and jostle. The pounding rhythm of the heart quickens. Blood rushes through arteries and veins at breakneck speed.
These changes begin as soon as pregnancy starts, and are fueled by a variety of hormones. The embryo implants in the uterine lining just days after fertilisation.
Since its DNA differs from that of its mother, the immune system should identify it as an invader, strike, and kill it, much as bacteria or other harmful microbes would.
That is the problem: the mother’s immune system must defend both her and the foetus, but it is unable to do so normally. What happens isn’t as easy as the immune response being reduced.
Instead, it’s a complicated interaction that we’re only beginning to grasp, involving a variety of immune cells, some of which appear to protect the foetus from other immune cells.
The body also forms an antibacterial mucus plug on the cervix, which holds germs at bay and seals the cervix before labour begins. The uterus extends upward and outward with the rising foetus as the pregnancy progresses.
Progesterone and relaxing hormones signal muscles to loosen in order to make room. The muscles that propel food and waste through the digestive tract relax, making them sluggish and causing constipation as the tract’s passage slows.
Heartburn and reflux may be caused by loose muscles at the top of the stomach allowing acid to escape into the oesophagus and throat. Morning sickness, which is caused in part by the hormone HCG, can be made worse by these changes, and it can also occur at other times of the day.
The diaphragm, the muscle that expands and contracts the chest with each breath, is pushed on by the uterus as it develops. This restricts the diaphragm’s range of motion. To compensate, the hormone progesterone serves as a respiratory stimulant, causing the pregnant woman to breathe faster, allowing her and the baby to get enough oxygen while having a smaller lung capacity.
All of this will make a pregnant woman feel out of breath. Meanwhile, the kidneys produce more erythropoietin, a hormone that promotes the development of red blood cells. To increase the amount of the blood, the kidneys store extra water and salt rather than filtering it out by urine.
The blood volume of a pregnant woman rises by 50% or more. However, since it just has 25% more red blood cells, it’s a little diluted. Normally, iron from our diet is used by the body to produce blood cells.
During pregnancy, however, the foetus builds its own blood supply from nutrients in the mother’s diet, leaving the mother with fewer iron and other nutrients. To pump all of this blood into the body and placenta, the heart needs to work extra hard.
While a pregnant woman’s heart rate rises, we don’t fully understand how blood pressure changes during a healthy pregnancy—a significant area of study because the heart and blood pressure are linked to some of the most severe complications.
The uterus’s expanding size can put pressure on veins, causing fluid to accumulate in the legs and feet. If it presses on the inferior vena cava, a broad vein, it can prevent blood from returning to the heart, resulting in a dizzying drop in blood pressure after a long period of standing.
Even before birth, some of these changes begin to reverse. The foetus drops down shortly before birth, relieving pressure on the diaphragm and enabling the pregnant woman to take deeper breaths.
When the water splits during labour and delivery, all of the extra fluid in the body is lost. In the weeks following delivery, the uterus shrinks again. Pregnancy affects the brain in the same way it affects the rest of the body, but the consequences are less well known.
Recent research has discovered variations in brain scans following pregnancy and early parenting, implying that these changes are adaptive. Since babies cannot communicate, they may be able to assist with parenting skills such as improved ability to read facial signals.
The scarcity of data on pregnancy’s impact on the brain illustrates a general truth: almost all pregnancy research has traditionally concentrated on the foetus rather than pregnant women.
Pregnancy experiences vary greatly, both within the context of safe pregnancies and due to complicating health conditions; new research will help us understand why and improve successful therapies where they are needed.
Meanwhile, since every pregnancy is unique, it’s important to seek medical advice if you have any serious concerns. Today, we’re on the verge of a breakthrough, when more attention is being paid to the fascinating biology of pregnancy.