and the ability to smell begins. Fetus can suck and swallow, to help develop the gastrointestinal (GI) system. Plus, it can also hic-hic-hiccup and even breathe, which is really helpful if it is born this early, since 90 percent will survive. Size: 1,100 grams, or the weight of one pineapple.
34 WEEKS
Skin is red and crinkled. Fat starts to be deposited to round out fetus. Reflexes like blinking and grasping are set, and the fetus is actually settling into noticeable sleep patterns. Size: 1,800 grams, or the size of the average Chihuahua.
36 WEEKS
If it hasn’t already, baby begins the descent into the pelvis to prepare for delivery. Fingernails reach the end of the fingertips.
37 WEEKS
Lungs are considered mature, and baby is not considered premature if delivered. This is considered full-term.
38 WEEKS
With formation of more fat, body becomes more rotund, less wrinkly. Size: 2,500 grams, or the weight of a lightweight laptop computer.
40 WEEKS
Normal gestation period ends. All systems go.
2 Feeding Time The Delicate Role of the Placenta in the Development of Your Child
Some miracles come in the form of avoiding a natural disaster, and some come in the form of making a championship-winning shot. But we believe that one of the most miraculous processes in the human body (and there are many) is how a mother’s body interacts with a baby’s during pregnancy. That miracle centers around an organ that may elicit gasps of eeeeew from the weak-stomached men in your life: the placenta.
This amazing, essential, and delicate system of tissues plays a huge role in influencing the health of your child. How? The placenta delivers nutrients and oxygen to the growing fetus, removes carbon dioxide and other waste, and provides the fetus with its early immunities. As the physical interface between the fetus and the mother, the placenta is where you are most literally bonded to your baby.
The flip side of that beautiful bond is that everything you do—the vapors you inhale, the toxins you expose yourself to, the cucumber-and-cookie sandwich you crave—can be passed on to your child through that miraculous organ.
The placenta, as you’ll learn in this chapter, has one big job: to preserve and protect the fetus. Typically, it does a darn good job, especially when facing challenges shared by our pregnant Paleolithic ancestors, such as infections and natural toxins.
But the reality is that it’s not always equipped to handle all of the things that we’re seeing in today’s diets and environment. In this chapter, we’ll explain why and how you can take an active role in protecting your baby, starting right about now.
The Point of the Placenta:
Formation and Function
Unless you’re starring in Alien, the general rule about organ development is that all of your organs are formed in utero, and that’s the set you live with. There aren’t too many instances of new organs or organlike substances appearing on a whim (unless you count fat, tumors, and the regenerative liver). But there is one big exception: the placenta. As we explain below, you can think of it as a kind of an organ transplant from your fetus to you that forms naturally inside you.*
Here’s how the magic works. After conception, the fertilized egg (now called the blastocyst) meanders to the end of your Fallopian tube and enters your uterus, searching for the uterine wall. As we stated in the previous chapter, this trip is the most dangerous trip any human being ever takes, because if the blastocyst does not implant successfully within seven days of conception, the uterine lining will be shed, and you’ll never even know you were pregnant. If it does, the placenta will begin to form at the point of attachment. Generally, the placenta starts to develop about a week after conception. If you take a look at figure 2.1, you’ll see that the blastocyst is made up of two layers: an inner cell mass and an outer layer. The inner cell mass is what becomes the embryo; the outer layer is what forms the fetal side of the placenta.
When the blastocyst implants in the uterine wall, the cells from that outer layer begin to form what are called chorionic villi. These villi, which look like coral reefs, carry blood vessels that go from the placenta into the spongy uterine wall, and it’s through the walls of those blood vessels that nutrients and waste are exchanged. A pool of maternal blood, called a blood lake, surrounds the villi. Your blood pressure forces blood through this lake and around the villi so they can absorb and pass needed nutrients and antibodies for immunity to your baby, and transfer the baby’s waste products to your circulatory system for disposal. During this process, there is no direct blood-to-blood contact between mother and child. About the same time that the placenta is forming, your hormones stimulate the inside layer of your uterus—already rich with blood vessels—to grow those vessels larger to facilitate the exchange.
Figure 2.1 Natural Resource Shortly after conception, the cells of the blastocyst need to find a way to absorb mom’s nutrients. So the outer layer of cells forms part of the placenta, while the inner layer forms the foundation of the fetus itself.
Factoid: The fetus needs to have oxygen continually. Its placenta supplies enough for one to two minutes, so a fetus can essentially hold its breath for that long. When a woman is in labor and having contractions, the amount of blood in the placenta lake decreases. As contractions get longer, the baby’s heart rate decelerates, providing a way to gauge fetal oxygen levels during delivery.
Factoid: Despite the small size of the placenta, the surface area of the villi is remarkably large. With about 700,000 villi, the surface area available for exchange is approximately the size of a one-bedroom house.
Once the placenta is fully formed and attached to the uterine wall (about the end of the first trimester), you can see a distinct difference between the maternal territory and the fetal territory. The maternal side is red and bumpy, from the shape of the villi poking through, while the fetal side is like a skating rink: smooth and slick, with the umbilical cord projecting from the surface.
But to think that the placenta is a one-trick pregnancy pony would be a mistake. Besides filtering and exchanging nutrients and gases, it has other duties, including making and secreting many hormones. Some of these include:
Estrogen: In pregnancy, estrogen stimulates the growth of the uterus and improves blood flow between the uterus and placenta. It also preps the breasts for milk production by enlarging a woman’s milk ducts. Estrogen secretion peaks right before birth.
The Truth About Miscarriages
There are typically four broad categories of reasons why women miscarry: One, the fetus has some kind of developmental defect or genetic abnormality that is incompatible with survival. Two, the woman has some kind of medical issue that diminishes the ability of the placenta to get nutrients to the baby; for instance, conditions like the immune disease lupus and connective tissue disorders tend to destroy the placenta. Three, the woman has a hormonal imbalance that prevents the corpus luteum from successfully supporting the fetus during the first trimester. And four, the maternal immune system can overreact and reject the fetus.
One miscarriage isn’t usually enough to concern docs about your future ability to carry babies. But after three miscarriages, docs will perform a full medical workup to try