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From Womb to Delivery Room

A Look at Embryo Development

By Renee Roberson

Seven weeks into pregnancy, the baby's genitalia will begin to differentiate. If you're carrying a boy, the scrotum and penis start to form. In a girl, the vulva develops first, then the clitoris. Eight weeks after conception, the baby has eyes, ears, mouth, lips, tongue, arms, fingers, knees and toes and is about 3 or 4 inches in length, Dr. Schapiro says.

"The early growth in the first trimester is primarily cellular," Buxton says. "It is a very sensitive period of development. Over-the-counter medicines, including ibuprofen, certain types of antibiotics, prescription medications, herbs and supplements can be harmful at this stage."

Dr. Schapiro says the embryo grows rapidly at 1 millimeter a day during the first eight weeks. At 11 weeks gestational age, the embryo can now be called a fetus. The baby smiles, frowns and even urinates.

"In the second and third trimester, there is less of a danger in taking over-the-counter medicines," Dr. Schapiro says. "The baby is getting hair on the head, eyes and eyebrows, fingernails and toenails are forming, and it is mostly just gaining weight and length at this point. Many specialists believe babies begin to hear around 24 weeks, so playing your baby classical music through your tummy before then may not do much good.

Want to see more?

• Conception from the Beginning: Reexamining the Birds and the Bees
• What's the Difference? Fraternal vs. Identical Twins
• First Trimester: Too Much Information? Getting Back to Basics in the First Trimester
• Check out our Article Library.
• Talk about it!

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