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Have you ever wondered how in 9 months, your body can create a perfect baby beginning from just one single cell? It's incredible! The average pregnancy lasts approximately 40 weeks and each week monumental progression takes place to create your little one. In this blog, we will take you along an outline of what the process looks like for your baby at each stage of the pregnancy.
Week 1 - 5
During this time your fertilized cell is called a zygote. During this time, cells are splitting and multiplying to make a gamete. This is the stage where all 46 normal human chromosomes are together. The cells keep dividing and forming different types of cell clusters that will become your baby! Your fertilized cells then travel from your fallopian tubes and into the uterus where the pregnancy will grow and implants. This stage is called the pre-embryonic stage. For the next 12 weeks, you will be classified as your first trimester.
Week 2 through week 8 are called the embryonic stage. Organogenesis happens, which is the forming of all major systems from this cluster of cells. Around day 15, there is a head and tail end of the baby formed. By week 4 the brain and spinal cord are developing, and limbs are beginning to bud. Around 28 days, the heart begins beating, and the mouth and digestive tract form. In week 5, the brain and heart now have more individual parts they need, and cranial and muscle nerves are present.
Week 6 - 12
In week 6, basic bone structure is present, and the baby is forming the means to
breathe and hear. The skull and jaws begin to form, and the baby produces red blood cells. The sex glands are now formed. At 7 weeks, you can now hear the heartbeat with an ultrasound! The tongue and stomach are forming. The bladder, urethra, and rectum separate from each other. The eyes continue to develop and the testes or ovaries begin to form. By 8 weeks, there are hands, feet, fingers, and toes. The bones and muscles are defining and movement is possible. The heart is complete and can be heard with a Doppler around this time. The ears are almost complete and fetal circulation begins.
From week 8 to birth is now called the fetal stage. Baby development begins to take place in larger stages. During this time, the weight gain of the baby increases, eyelids meet and fuse, swallowing happens, the baby can urinate, fingernails develop, and the placenta begins to take over sustaining life for your baby. Your uterus is beginning to rise above your pubic bone.
Photo Credit: Growth Development and Ageing by David A Jones, 12 wk fetus
Week 13 - 20
Welcome to the second trimester! During weeks 12-16, there is rapid skeletal development. Fine hairs called lanugo begin to be present on your baby’s body. Head hair begins to form, meconium or the first poop is present in the bowels, and the external sex organs are identifiable by ultrasound.
During weeks 16-20, a thick white coating forms on the skin called vernix. Baby will continue to gain weight, adding brown fat around the shoulders and back which will keep them warm and fed once they are born until your milk comes in. Fetal heart tones can be heard with a fetoscope, and baby movement can be felt. Teeth and toenails form and the spinal cord continues to develop. By this point, your uterus is about at your belly button.
Photo Credit: Baby Center, 16wk fetus in utero
Week 21 - 28
During weeks 20-24, most organs are completed and functioning and both teeth and ears continue to form. The baby responds to sound around 24 weeks, and the skin is red and wrinkled. This is also when they develop sleep and wake cycles and their movements become more time-able.
24 weeks can be the youngest gestational age of viability outside of the womb due to the reparatory and nervous systems being developed. The baby is very active by 28 weeks with their eyes now opening, eyebrows and eyelashes, and fingernails present. From here forward, your uterus will measure roughly how many weeks pregnant you are and continue to rise until birth.
28 weeks marks the third and final trimester!
Photo Credit: Baby Center, 24wk fetus
Week 29 - Birth
During weeks 29-36, the baby’s skin gets lighter and less wrinkled and lanugo disappears from the face. Testes descend in male babies. More reflexes are present. Around 32-36 weeks, weight gain is 25 grams a day on average, and the baby gets rounder while lanugo disappears from the body. Lots of vernix still covers the skin and head hair and nails continue growing. The ear cartilage is soft, and the feet and hands are showing more creases.
During these last weeks, optimal weight gain for the baby is being achieved. The
respiratory movements are more frequent, and the average weight is 6-9 lbs. Relaxin a hormone that helps relax muscles and bones is working in the mother’s body to help the cervix soften and thin. The baby engages in the pelvis, and stretch receptors trigger practice contractions called Braxton Hicks. In individuals who have already had a baby, Braxton Hicks can start much earlier. Oxytocin and receptor sites are increasing and the mucus plug may be released.
Photo Credit: Baby Center, 36wk fetus
Sources:
Jordan, R. G., Farley, C. L., & Grace, T. K. (2018). Prenatal and postnatal care: A woman-centered approach (2nd ed.). Wiley-Blackwell. p 33-46.
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