Your baby is just half of what your doctor checks during routine ultrasounds. That's because you're not just growing a baby — you're growing a one-stop shop for all your baby's needs: the placenta.
While your baby grows and matures over nine months of pregnancy, there’s something else growing in your uterus too — and it’s responsible for keeping your baby alive. You’ve likely already heard of the placenta, but what does it do? And what do you need to know about it to have a healthy pregnancy?
SO WHAT IS THE PLACENTA?
The placenta is the lifeline between your baby (or babies!) and your own blood supply. Through all stages of pregnancy, it lets your baby eat and breathe — with your help, of course. The connection is also why consuming substances such as alcoholand caffeine can impact your baby.
To grow, your baby needs nutrients, water, oxygen, antibodies against diseases, and a way to get rid of unneeded waste like carbon dioxide. The placenta provides all of these. As your own blood flows through your uterus, the placenta seeps up nutrients, immune molecules and oxygen molecules circulating through your system. It shuttles these across the amniotic sac — through the umbilical cord that connects placenta to baby — and into your baby’s blood vessels. Likewise, when your baby builds up carbon dioxide or other things he or she doesn’t need, the placenta passes these back to your blood.
The placenta also acts as a barrier — it’s vital that germs in your body don’t make your baby sick and also that your body doesn’t reject your baby as foreign material. So at the same time the placenta allows blood cells and nutrients through, it keeps most (but not all) bacteria and viruses out of the womb and also prevents many of your baby’s cells from entering your bloodstream (where they might set off alarms).
In recent years, doctors and scientists have discovered that your placenta has even more functions than they’d known about in the past. Rather than just being a passive bridge between you and your baby, the placenta also produces hormones and signaling molecules, such as human placental lactogen (HPL), relaxin, oxytocin, progesterone and estrogen, which are necessary for both of you during pregnancy. Some of these molecules encourage new blood vessels to form — both between your body and the placenta, and between the placenta and your baby — to carry oxygen to the fetus, some help your body prepare to make milk (but also prevent you from lactating before you give birth), and others boost your metabolism to help supply energy to both you and your growing baby.
WHERE IT COMES FROM
After an egg is released to be fertilized around week 3 of pregnancy, the follicle in the ovary that it came from — called the corpus luteum — collapses, starts producing the hormone progesterone, and provides nourishment and support for an embryo throughout the first trimester of pregnancy.
Meanwhile, seven or eight days after a sperm fertilizes an egg inweek 4 of pregnancy, a mass of cells — the earliest form of an embryo — implants into the wall of the uterus. Some cells from this mass split away, burrowing deeper into the uterine wall. Instead of preparing to form fingers and toes and a brain like the rest of the embryo’s cells, these ones are destined to form a disc-shaped organ that’s chock-full of blood vessels and will take over for the corpus luteum in the second trimester: the placenta.
If you have fraternal twins, each baby will have its own placenta. With identical twins, whether you have one or two placentas depends on when the fertilized egg splits — if the placenta has already formed when the embryo split in two, one placenta will sustain both twins — they’ll each have an umbilical cord linking them to the shared placenta. If the split happened earlier, though, you may have two placentas — one for each baby.
Over the next two months, the placenta develops. Small capillaries turn into larger vessels, providing your growing baby with more oxygen and nutrients. By week 12 of pregnancy, your placenta has all the structures it needs to step in for the corpus luteum and sustain your baby for the rest of pregnancy — although it will continue to grow larger as your baby grows. By the time you’re full-term at 40 weeks pregnant, your placenta will, on average, weigh about a pound.
POTENTIAL PROBLEMS & MONITORING THE PLACENTA
To remain fully functioning and grow at the right pace, a placenta requires the same healthy lifestyle as your baby — which means smoking or using illegal drugs can negatively impact it. But even if you follow every rule for a healthy pregnancy, things can go wrong with the placenta due to genetics — or just chance.
Other factors that can influence placental health include maternal age, blood pressure, previous cesarean sections and being pregnant with multiples. If you experience vaginal bleeding, severe abdominal or back pain or rapid uterine contractions (when you’re not full term), talk to your medical practitioner as these could be signs of placental problems.
Otherwise, your medical practitioner will be on the lookout for any abnormalities with the position and size of your placenta during your ultrasounds. He or she might notice that you have ananterior placenta, placenta previa, enlarged placenta, placental abruption or placenta accreta. In most cases, these conditions just mean that your doctor will keep an extra eye on your pregnancy, since the placenta can have a wide variety of sizes and positions and still do its job.
Scientists have also discovered that since the placenta shares genes with your baby, its appearance or molecular properties might provide early signs of other conditions includingpreeclampsia, premature birth, genetic diseases and even autism. As they begin to understand these links better, tests related to placental health may become more common.
DELIVERING THE PLACENTA
When you finally give birth to your baby, the last thing on your mind is the placenta that remains inside your uterus. But now that your baby is out and the umbilical cord is cut, the placenta has no use (a new one will develop with every future pregnancy). That means after you deliver you baby, you also need to deliver the placenta (called stage three of childbirth). You’ll continue to havecontractions, and your practitioner may speed along the placenta delivery by pulling gently on the umbilical cord or massaging your uterus. Whether you keep the placenta as a memento, eat it or let your practitioner take it away is up to you — and your birthing center’s policies.
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