Muscles and joints shift and jostle. The heart’s pounding rhythm speeds up. Blood roars through arteries and veins. Welcome to pregnancy, ladies.
Over the course of a pregnancy, every organ in the body changes. Ignited by a range of hormones, these changes begin as soon as pregnancy begins. That can happen when a sperm, which is produced in the testicles, combines with and fertilizes an egg, which is produced in the ovaries.
If a fertilized egg attaches to the wall of the uterus, the process of pregnancy has begun. But before we touch upon the process and effects of pregnancy, I must ask — how do the sperm & egg meet?
Sperm & Egg: A Love Story
The most common way for a sperm and egg to meet is during sexual intercourse, a.k.a when a penis is inserted into a vagina. Semen, which is a fluid that carries sperm is ejaculated and then swims up through the cervix and uterus and travels to the fallopian tubes hopefully to find an egg. If the egg and sperm unite, travel down to the uterus together, and implant in the uterine wall, then the process of pregnancy has begun.
Some people get pregnant with the help of a doctor through a process called artificial insemination. This is when semen is injected into the cervix or uterus by a healthcare provider. The sperm must travel up to the fallopian tube and unite with an egg. The fertilized egg travels down the fallopian tube to the uterus and implants in the wall so that the process of pregnancy can begin.
Alternatively, doctors can bring sperm and egg together completely outside of the body in a laboratory and then later insert the fertilized egg into the uterus. This process is called in vitro fertilization. All of these methods may lead to pregnancy. Over the course of nine months, the fertilized egg grows into a fetus and develops organs and bodily functions until it’s ready to be born. Sounds so simple, yet it’s one of the most complex and magical processes the female body can ever endure.
So, what happens to the female body?
Just days after fertilization, the embryo implants in the lining of the uterus. Because its DNA doesn’t exactly match the mother’s, the immune system should theoretically recognize it as an invader — attack and destroy it like it would with bacteria or other harmful microbes.
That’s the challenge: the mother’s immune system needs to protect both her and the fetus, but can’t act as it usually does. What happens is not as simple as decreasing the immune response. Instead, it’s a complex interaction we’re just beginning to understand, involving many types of immune cells — some of which seem to protect the fetus from attack by other immune cells. The body also creates an antibacterial plug made of mucus on the cervix, which keeps germs away and stays sealed until labor.
As pregnancy progresses, the uterus expands upward and outward with the growing fetus. To make room, hormones called progesterone and relaxin signal muscles to loosen. The muscles that propel food and waste through the digestive tract also loosen, which makes them sluggish, causing constipation. Loosened muscles at the top of the stomach might allow acid to escape into the esophagus and throat, causing heartburn and reflux. These changes can worsen morning sickness, which is caused in part by the hormone HCG — and can also happen at other times of the day.
As the uterus grows, it pushes on the diaphragm, the muscle that expands and contracts the chest with each breath. This limits the diaphragm’s range. To compensate, the hormone progesterone acts as a respiratory stimulant, making the pregnant woman breathe faster so both she and the baby can get enough oxygen with less lung capacity. This all may leave the pregnant woman feeling short of breath.
Meanwhile, the kidneys make more erythropoietin, a hormone that increases red blood cell production. The kidneys also keep extra water and salt rather than filtering it out into urine to build up the volume of the blood. A pregnant woman’s blood volume increases by 50% or more, yet it’s also a bit diluted because it only has 25% more red blood cells. Usually, the body makes blood cells using iron from our food. But during pregnancy, the fetus is also building its blood supply from nutrients in the mother’s food — leaving less iron and other nutrients for the mother.
The heart has to work extra hard to pump all this blood through the body and placenta. A pregnant woman’s heart rate increases, but we don’t fully understand how blood pressure changes in a healthy pregnancy, because some of the most serious complications are related to the heart and blood pressure. Furthermore, the expanding uterus may press on veins, causing fluid buildup in the legs and feet. If it presses on a large vein called the inferior vena cava, it might interfere with blood returning to the heart, causing a dizzying drop in blood pressure after standing for too long.
Some of these changes start to reverse even before birth. Shortly before delivery, the fetus drops down, decreasing the pressure on the diaphragm and allowing the pregnant woman to take deeper breaths. During labor and birth, much of the extra fluid in the body is lost when the water breaks. The uterus shrinks back down in weeks after birth.
Like the rest of the body, pregnancy affects the brain — but its effects here are some of the least understood. Recent studies show differences in brain scans after pregnancy and early parenting and suggest that these changes are adaptive. That means they could help with parenting skills, such as an increased ability to read facial cues since babies can’t talk.
All in all, the lack of information about pregnancy’s effects on the brain highlights a general truth: historically, almost all the research around pregnancy has focused on the fetus, rather than the pregnant women. Hopefully, this will change. In the meantime, every pregnancy is different, and it’s important to consult a doctor with any specific questions. So what’s your experience with pregnancy been like? I would love to hear your stories down below!