In Depth Baby Product Reviews Led by a Pediatrician

Building Marrow

Fat, bone marrow, and brain growth make this a big week
Building Marrow
Credit: Lorelyn Medina ©
Wednesday October 16, 2019

At 30 weeks, the baby is around 11 inches and somewhere between 2.5 and 4 pounds. Even though you already feel like an overstuffed sack of potatoes, the baby is putting on about 17 ounces a week, so you will continue to grow as the baby does. Boy babies' testicles will begin their descent, and girls' labia will continue to develop, making biological gender identification a no-brainer.

At this stage, the baby is hard at work building the support system for life, and this is when all the details start to come together:

  • Bone Marrow Production — Interestingly, the baby's bone marrow is also making a pretty significant change around 30 weeks by taking over the production of red blood cells from the spleen and other tissues. This shift in red blood cell creation location will give her a better chance of survival if she is born after week 30. While no one wants to think about having a preterm infant, it is something of a milestone to make it this far in your pregnancy.

  • White Fat Accumulation — A layer of white fat is forming to promote temperature regulation upon birth.

  • Brain Growth — Your baby's brain is growing larger and more sophisticated by the day at this point with the development of grooves and wrinkles increasing its surface area for adequate storage space for all of the new input and skills that the baby will soak up once born.

References Sources

  1. I'm Pregnant!: A Week-by-Week Guide from Conception to Birth
  1. Mayo Clinic Guide to a Healthy Pregnancy
  1. WebMD - Your Pregnancy Week by Week: Weeks 26-30

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