Charlotte Lozier Institute

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Week 13

Complex facial features and behaviors

Human Prenatal Age
  • Post-conception Week 11
  • Days 70-76
  • 3 Months Pregnant
  • Gestational Week 13
  • The fetus practices breathing in the womb. Usually, she waits 2 to 3 seconds between breaths.1

  • The fetus starts producing enkephalins, neurotransmitters specific to the transmission of pain.2

  • Antibodies from the mother may pass to the fetus.3

  • The fetal heart pumps about 6 quarts of blood per day.4

This week, the lips and nose have matured into their adult shape.5 Now the preborn child has complex facial features. Furthermore, the vocal cords start developing.6 Later in the pregnancy researchers will even see the vocal cords vibrate as the fetus practices crying in the womb.7

When can antibodies pass from the mother to the fetus?

During the pregnancy, maternal antibodies can transfer to the developing fetus. The earliest evidence of antibodies entering the fetal blood is from a study of fetuses as young as 13 weeks gestation.8 The number of antibodies in the fetus’ bloodstream rises continuously from 17 weeks until birth, with the sharpest increases in the last month of pregnancy.9 At birth, the baby usually has a higher concentration of antibodies than the mother to keep the baby from catching dangerous diseases.10

During an ultrasound, a mother may be surprised to see her baby kicking and swallowing amniotic fluid, even through she cannot yet feel these movements. (Image Credit: Priests for Life)
Does the baby pee in the womb?

Yes! In week 13, the fetus starts urinating into the amniotic cavity. By the last month of pregnancy, the fetus actually excretes half a liter of urine every day.11  Around 13 weeks, the fetal intestine begins to absorb water and glucose from amniotic fluid that the fetus swallows, too.12 Furthermore, the fetus’s respiratory tract also absorbs much of the water that the fetus swallows. Therefore, it is highly important that the amniotic fluid gets recycled quickly. In fact, the water content of amniotic fluid completely changes every three hours!13

How does the face form?

The major components of the face arise from two important tissue types – pharyngeal arches and neural crest cells. In the developing embryo, there are six pharyngeal arches.  The pharyngeal arches form from mesoderm around six weeks gestation. Each pharyngeal arch has its own blood vessel, cranial nerve, and bar of cartilage which will later form bones. Neural crest cells are special cells that come from areas next to the neural tube.14

Between 6 and 8 weeks, a set of neural crest cells grows quickly to make the frontonasal prominence. This area of the developing face becomes the nose and forehead. The first phayrngeal arch also develops into the jaw, lips, cheeks, and outer ears. By 8 weeks the face is mostly developed, but the nostrils are very large and the left and right cheeks are completely separate from one another – there is no upper lip area yet. By 12 weeks, the tissue of the cheeks has fused together under the nose forming the upper lip allowing for unique differences in facial identity.15

Dive Deeper
Researchers have seen maternal antibodies in the umbilical cord as early as 8 to 10 weeks gestation...