The skeletal and nervous system have made enough connections to signal movements of the limbs and body. In addition, your baby’s facial muscles are now well enough developed to allow for a variety of expressions. Inside your uterus, your baby may be squinting or frowning at you, although these movements aren’t conscious expressions of emotions. Your baby’s skeletal system continues to develop as more calcium is deposited on the bones.
If you're having a girl, millions ot eggs are forming in her ovaries this week. Beginning at 16 weeks, your baby’s eyes are sensitive to light. Although you probably don’t even know it, your baby may be having frequent bouts of the hiccups. Hiccups often develop before your baby performs lung movements associated with breathing. Because your baby’s trachea is filled with fluid rather than air, the hiccups don’t make that characteristic hiccup sound.
You may feel your baby’s first movements around this time. These early movements are like a fluttering, bubbling sensation. You may notice the beginning of the linea nigra, a dark line which appears down the centre of your abdomen. This will disappear after the birth.
The baby will be moving around frequently now, although you may have only just started to feel this. The body will became covered in a fine downy hair called lanugo, which is thought to maintain the right body temperature. It is possible to tell a baby's sex now through an ultrasound scan. When 16 weeks pregnant, the baby is around 4.6 inches (11,5 cm) long and weighs around 3.5 ounces (105 grams).