Everything you need to know about the uterus

At only 3 inches long and weighing just 60 grams, its role far outweighs its size.

Despite being the source of all life, the uterus or womb isn’t a flashy, attention-seeking organ. At only 3 inches long and weighing just 60 grams, its role far outweighs its size. Sitting pretty, tucked away behind the bladder, it allows 211 million women to get pregnant every year, but is also the source of pain, bleeding and conditions like endometriosis. For an organ so vital to motherhood, it’s likely you don’t know much about your own beyond what gynaecology appointments have revealed.

From abandoned theories about the uterus travelling around the body and causing hysteria, we now know the uterus sits low in the abdomen, and stays there thanks to the muscles and ligaments holding it in place. It is connected to the vagina by the cervix and receives unfertilised eggs from the ovaries via the fallopian tubes, which are connected to both sides of the uterus. The uterine wall comprises the endometrium, which thickens and sloughs during the menstrual cycle, the myometrium, the muscle layer, and the perimetrium, which covers the outer surface of the uterus. The uterus accepts a fertilised egg, which implants in the endometrium and derives nourishment from the placenta, which grows for this purpose. As the baby grows, the uterus stretches more than 500 times its original size to accommodate it, producing the bump. The uterus is a baby’s first home and returns to normal within six weeks after birth. While it’ll appear the same as before, it’ll be slightly roomier after your first pregnancy, and the muscles will be more toned and flexible— thanks to the workout they just went through— which is why second pregnancies may show sooner and labour may be easier and quicker.

Unfortunately, no-one knows. There are theories, and a 2015 paper compiled plenty of studies to confirm we have far more questions than answers. We know that a decline in progesterone triggers menstruation and that the endometrial coagulation system is part of what stops the bleeding. But we don’t know exactly what causes the bleeding to stop, what regulates inflammation during a period, or how the uterus repairs itself without creating any scar tissue. We don’t even know why we bleed in the first place. While live birth is a part of the mammalian experience, only humans, fruit bats and elephant shrews menstruate on a regular basis. All other animals reabsorb the endometrium. One theory is that menstruation protects us from abnormal pregnancies; as human gestation takes so long and requires so many biological resources, rejecting all but the most viable could be a protective feature.

Also known as a retroverted or retroflexed uterus, 20 to 30 percent of all women are the proud owners of a tilted uterus. In the rest of the population, the uterus tips forward and points towards the stomach or straight up; when a uterus is tilted, it points towards the back instead. This is nothing to worry about and is simply a ‘normal anatomical variance’ caused in most cases by your genetics. In some rare cases, some women develop a tilted uterus when the ligaments that hold their uterus in place have become weakened during pregnancy, or due to complications with fibroids or endometriosis. A tilted uterus is unlikely to give you any side effects or display any symptoms other than some difficulty using tampons in some women—as such, you’ll likely not know if you have one until the discovery is made during a gynaecological exam. You certainly won’t need to worry about it affecting your fertility, as a woman with a tilted uterus is just as likely to conceive as anyone else, and during pregnancy, the only differences you might encounter would be an increase in back pain, or the uterus leaning on your bladder, making it hard to fully empty. By the tenth or twelfth week, a titled uterus will typically straighten out as the uterus ‘pops’ forward into the abdomen to accommodate your growing baby. You’ll most likely also have a completely normal labour and birth experience as it’s extremely rare a tilted uterus will cause any difficulty delivering.

Most uteruses are shaped like an upsidedown pear, with the fallopian tubes attached to the widest part on either side at the top. A heart-shaped uterus looks like it sounds: the main uterine cavity—the fundus, where the baby develops—features a little indent at the top where the two fallopian tubes meet. It’s a simple uterine anomaly affecting just one to two percent of women, and having one isn’t necessarily a bad thing. Many women will go their entire lives unaware of their heartshaped uterus as it has no symptoms or effects on your periods—in rare cases, you may be at higher risk for endometriosis—but your risk of preterm delivery or breech delivery is increased. Fear not though: if you do have a heart-shaped uterus, a pregnancy that’s closely monitored will be just as likely to be successful as any other.

The placenta is a transient organ created only during pregnancy. It is one of the least studied and least understood organs, and could hold the secrets to enhancing immunology and transplant medicine. The placenta acts as the lungs, kidneys, and liver for the baby, as well as the gastrointestinal, endocrine and immune systems. It feeds and protects the baby from infections and the mother’s immune response, while extracting the blood-soluble waste the foetus produces. Weighing around 500g, it’s about as thick as a medium-sized steak with a smooth surface where the baby grows and a rough side that attaches it to the womb. Following childbirth, you need to then pass the placenta as it detaches from the uterus— as the womb contracts to deliver the baby, the placenta becomes strangulated between the three layers forming the uterine wall. Once the baby is born, the uterus continues contracting, but the placenta can’t change its shape or size, no longer fits, and begins to separate. Out comes the placenta; and yes, people do eat it post-birth.

When it functions normally, the placenta provides the baby with a constant stream of nutrients and oxygen, but when things go wrong with the placenta, they really go wrong. If it’s under-invasive, its connection to the mother’s blood isn’t strong enough, meaning the baby won’t be getting the nutrients it needs to develop, and this could lead to preeclampsia. If it’s over-invasive, it can infiltrate the uterus and other organs like a cancer. Finally, it can detach from the uterus before delivery, in a complication known as placental abruption, causing heavy bleeding in the mother and removing the source of the baby’s oxygen and nutrients.

The word 'placenta' means flat cake, named after its flat round shape, and it’s believed this is the inspiration behind the traditional round shape of a birthday cake!

Scientists are still discovering what a normal placenta is and how it functions, and new technologies are allowing us to safely study it during pregnancy. Learning more about the placenta could lead to new treatments to improve the health of the mother and child during pregnancy and provide insights into other areas of research including organ transplantation. ■

Your uterus allows a connection with your unborn baby. At around 18 to 25 weeks, your baby can hear and, while muffled, the sound that travels through the uterus is your baby’s first contact with the outside world, which is why you’re encouraged to talk to your bump. At just ten weeks old, your little foetus can feel your heartbeat, and that’s why your new-born can be comforted by resting on your chest—your heartbeat is a reminder of being in the womb.