Critical Periods in Your Unborn Baby’s Development

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Graduation. That first date. The wedding. Maybe that interview for a coveted job. There are so many big moments in our lives—moments that stick in our memories for a lifetime. And some of these events might even change our lives for good, so we want them to go well.

What we might not appreciate quite as much is that critical “moments” start before we’re born. Technically, they’re not just brief moments in time; rather, there are specified periods that need to go well in order to help ensure not only a healthy newborn baby, but also continued good growth and development into adulthood. Let’s examine this timeline in more detail.

Terms of Embryogenesis

It’s helpful to consider the period from conception to birth as a series of stages. The first stage is known as the germinal period. It begins after the sperm fertilizes the egg. This forms a cell called a zygote, which begins to divide, eventually forming a hollow ball of cells known as a blastocyst. The blastocyst ultimately reaches the uterus and attaches itself to the uterine wall. (If for some reason this course of events does not happen at this stage, there is no baby-to-be.)

Around this time, the ball begins to be called an embryo. It won’t be a ball for long, because the cells respond to cues from their surroundings to become different types of cells, which ultimately form organs and body parts. For example, the neural tube which encloses the future spine, spinal cord and brain closes around the 27th day of life. The beginnings of limbs (arms and legs) form around day 30, and the heart in its mature form around the 5th week. Thus, if something goes wrong during the embryonic period, the organs may not form correctly.

At about week 10 there’s another name change. The future infant now becomes known as a fetus. The organs are well formed at this point, and in many ways, the fetus actually begins to look like a little person! The challenge at this point is to make sure that the fetus continues to grow, and that certain organ systems that take longer to mature—probably most importantly, the brain and nervous system—are given the best opportunity to do so.

Challenges: Drugs, Infections, and More

When we know a little more about what develops when, it becomes easier to understand how the process can go wrong. One of the best-known examples was thalidomide, a drug used in the 1950s for morning sickness in pregnant women. Babies born to women who took the drug suffered from a variety of birth defects, the most prominent of which were deformed limbs. This drug was largely responsible for closer regulation of medications by governments worldwide. (Thalidomide has since become popular as a cancer treatment.)

Drugs like thalidomide, as well as certain infections like rubella (commonly known as “German measles”) exert their negative effects most in early pregnancy, although it’s a good idea to also prevent an older fetus from being exposed. Alcohol can also cause birth defects when ingested early on; however, many of alcohol’s more subtle effects show up in late-pregnancy drinkers. Children exposed in this manner may not have frank birth defects, but they will have problems achieving milestones and learning. Similarly, both cigarette and marijuana smoking may exert subtle effects on growth and development even when used after a baby’s organs are formed. They do this largely by affecting the delivery of nutrients to the unborn baby.

Not all birth defects come from drugs or infections. Spina bifida is a condition where the neural tube doesn’t close; the lower spine and spinal cord remain open to the outside. Nerve damage or even brain damage may occur. One cause is a lack of the vitamin folic acid in the diet early in pregnancy.

Keeping Your Unborn Baby Healthy

When it comes down to it, there is really no “non-critical” period in the life of a baby-to-be. Some medications are so detrimental to the embryo from the time of conception that physicians are only allowed to prescribe them to a woman if several methods of birth control are being used. And many maternal conditions—chicken pox or diabetes, for example—can cause problems either early in pregnancy or at birth. If you are planning to become pregnant (or not planning to not become pregnant), it’s important to know the risks of anything you might be taking, whether prescribed or recreational, and to avoid situations where you might pick up a harmful infection. And if you are pregnant, have that talk with your provider about factors that might affect your baby’s development. Knowing the “when” and “why” of your unborn baby’s development helps reinforce the “what to do.” And when early development goes well, there’s a better chance of growing up healthy and celebrating life’s other great milestones.

Stan Sack
Dr. Stan Sack has 29 years’ experience as a primary care pediatrician in Massachusetts and Florida. A medical writer since 2015, he enjoys blogging on topics that are on parents’ minds but are covered less often in books and on websites. He lives in the Florida Keys with his family and enjoys healthy cooking, fitness activities and singing in his spare time.

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