Week 12 (CRL= 87 mm)
The most significant development at this period is the determination of the fetal gender at the end of the twelfth week through the appearance of the fetal genitalia. Weight of the fetus is approximately 45 grams.
- NERVOUS: Brain surface is still smooth without grooves or sulci or gyri, otherwise known as convolutions.
- SENSORY: The nasal septum and palate development are already completed.
- CARDIO and RESPI: The heartbeat can now be detected using a Doppler transducer.
- DIGESTIVE: The sucking reflex is already present. The liver forms the bile at this period.
- GENITOURINARY: Urine production by the kidney is initiated. The external male and female genitalia can now be distinguished and differentiated by their appearances.
- MUSCULOSKELETAL: The limbs appear long and thin. At this point, the involuntary muscles of the viscera develop.
- INTEGUMENTARY: At the end of the twelfth week, the downy lanugo is developing.
Week 16 (CRL= 140 mm)
By the sixteenth week age of gestation, the fetal face looks human because the eyes are now facing fully forward. Quickening (fetal movements) are felt by pregnant mothers. Approximately, the fetus weighs 200 grams at this time.
- NERVOUS and SENSORY: The face of the fetus looks like a human because the eyes are facing forward rather than to the side.
- CARDIO and RESPI: Rapid development of the pulmonary vascular system is taking place.
- DIGESTIVE: Amniotic fluid is swallowed by the fetus at this point and meconium is now produced.
- GENITOURINARY: Urine is excreted into the amniotic fluid.
- MUSCULOSKELETAL: The lower limbs achieve its final relative length which is longer than the upper limbs. A multigravid pregnant woman may now begin to feel the fetal movements.
- INTEGUMENTARY: Adequate cartilages are present that enable the external ears to stand away from the head. Visible blood vessels are observed through the delicate fetal skin. At this point, the fingerprints are developing.