Baby Developing inside you

Fetal Development

Baby developing inside you
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baby 13 weeks pregnant inside


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Week Thirteen: Baby flexes and kicks

You are 13 weeks pregnant. (fetal age 11 weeks)
  • The fetus has grown to about 3 inches (8cm) long.
  • Weight approximately 1 ounce (25 grams).
  • Bone is beginning to replace cartilage and the ribs are appearing.
  • The nose and chin are well defined.
  • Movements can be measured.
  • The child will begin to learn to suck its thumb.
  • The child can open and close its mouth.
  • The external genitalia are almost defined, it may be possible to tell if baby is a boy or girl.


Your baby is now producing insulin the hormone that controls their blood glucose. The fetus is now 3 inches long and weighs about an ounce. The baby's unique fingerprints are already in place. The muscles lengthen and become organized. You can't feel it yet, but your baby can move in a jerky fashion, flexing the arms and kicking the legs.


Your uterus has grown quite a bit. You can probably feel its upper edge above the pubic bone in the lowest part of your abdomen, about 4 inches (10cm) below your bellybutton. At 13 weeks, your uterus fills your pelvis and starts growing upward into your abdomen. It feels like a soft, smooth ball. Soon you will start feeling the first flutters of the unborn child kicking and moving within.

The first three months were period of rapid development, next three months will be period of rapid growth. Baby quadruples weight during the 4th month. Your baby is now about 2.91 inches (7.4cm) and weighs around 0.81 ounce (23gm).

Week by week:   First trimester ultrasound scan pictures: Week 13

<<< Week 12  |  Month 3  |  Month 4  |  Week 14 >>>


Week By Week Pregnancy Calendar

First Trimester
Week 1   Week 2   Week 3   Week 4   Week 5   Week 6   Week 7  
Week 8   Week 9   Week 10   Week 11   Week 12   Week 13
Second Trimester
Week 14   Week 15   Week 16   Week 17   Week 18   Week 19   Week 20  
Week 21   Week 22   Week 23   Week 24   Week 25   Week 26
Third Trimester
Week 27   Week 28   Week 29   Week 30   Week 31   Week 32   Week 33  
Week 34   Week 35   Week 36   Week 37   Week 38   Week 39   Week 40