Week 13

By 13 weeks, the unborn baby frequently practices breathing in the womb. He often makes a few small rhythmic breathing movements followed by a pause of a few seconds.¹⁷ These gentle practice breaths are vitally important for the development of the unborn baby’s lungs.¹⁸ Fetal breathing movements help the lungs grow by increasing the number of lung cells and helping them develop into their proper types.¹⁹ Researchers have found that in twins, each baby’s breathing and general movements develop independently, showing that every child follows his own developmental rhythm.²⁰

The unborn baby’s breathing movements reflect his changing environment. Breathing movements usually increase in the early morning and after the mother eats.²¹ Healthy conditions support these essential breathing motions while smoking, alcohol, extreme stress and certain drugs can decrease them.²²

The kidneys filter toxins and excess salts out of the blood stream. Permanent kidney development begins around 7 weeks gestation.^{23 24} The kidneys contain many smaller filtering units, called nephrons, which help move toxins and salts from the blood into the urine. Between 8 and 12 weeks, approximately 20 functional nephrons form, allowing small amounts of fluid to be excreted into the amniotic fluid.²⁵ Nephron development continues through repeated branching until about the 34 week, reaching a total of 1 to 3 million—similar to the number found in fully developed adult kidneys.²⁶ Initially, around 8 weeks, the kidneys form right next to each other in the pelvis, below the tailbone. As the abdomen grows, the kidneys move up and farther apart, reaching their mature positions around 11 weeks gestation.²⁷

The face begins forming from the pharyngeal arches and neural crest cells. Around 6 weeks of pregnancy, six pairs of pharyngeal arches appear as small bulges in the neck. Each arch contains blood vessels, nerves, and cartilage that will later form bones. Neural crest cells are special cells that grow near the developing brain and help build much of the face.³⁴

Between 6 and 8 weeks, neural crest cells grow to form the forehead and nose. At the same time, the first pharyngeal arch forms the jaw, lips, cheeks, tongue, and outer ears. By 8 weeks, most parts of the face are present, but the nostrils are very large and the upper lip has not yet formed.³⁵ By 12 to 13 weeks, facial features can be seen on ultrasound.³⁶ The area between the lips and nose is the last area to fuse and form, around 16 weeks.³⁷ By 16 weeks, the face has taken on its familiar shape,³⁸ and all the muscles used in facial expressions have formed.³⁹ Even in the womb, the baby’s face is already unique, reflecting their individuality from the very beginning.