The First Trimester - What's Happening?

The beginning of pregnancy can be an exciting, scary, overwhelming, emotional time – especially for first time mothers. So…. What’s happening?

The First Trimester: Weeks 1-13


Mama’s Symptoms

  • You still don’t know you’re pregnant yet!!

Baby’s Development

  • Week 2-3  –  Ovulation and Fertilization

  • Week 3 – Blastocyst implantation – Cells are rapidly dividing, and are being nourished by a yolk sac (the cavity that provides nutrients before development of the placenta).  Cells that will soon be forming the placenta are beginning to produce hCG, the hormone that will give you a positive pregnancy test.

  • Week 4 –  Size of a poppyseed. Cells are dividing to become the embryo and placenta.  Neural tube, brain, and backbone have already formed. Amniotic sac and fluid are forming to create a protective cushion for your little one.


Mama’s Symptoms

  • You have probably just found out that you are pregnant – a missed period, swollen/sore breasts, bloating, and nausea are common symptoms of early pregnancy.

  • hCG levels are now detectable by a home pregnancy test.

  • You are having a MAJOR decrease in energy  – feeling exhausted all the time is normal, due to major hormonal changes.

  • These hormonal changes will also cause a heightened sense of smell!

  • Feeling gassy is unfortunately common throughout pregnancy – farting, burping, and hiccuping are part of the fun of pregnancy.

  • Soon your hormones will also trigger sudden mood swings – don’t be surprised if you find yourself suddenly bursting into tears during movies, or becoming angry at your partner over something trivial.

  • During the first trimester, you may be surprised to already have to pee constantly! This is not due to pressure on the bladder, but is because your blood volume is rapidly increasing; there is now a lot of extra fluid that ends up in your bladder.

Baby’s Development

  • Week 5Size of an apple seed.  Baby is now an embryo. Major organs are starting to form (heart, liver, kidneys, stomach)

  • Week 6Size of a pea.  (1/4”)  Circulatory system, nose, eyes, & ears are developing!  Baby has tiny paddle-like hands with webbed fingers. Baby’s heart rate is about twice as fast as yours, and the chambers are beginning to divide.

  • Week 7Size of a blueberry (1/2”)  Brain cells are rapidly developing, as the arm and leg joints are forming. Baby now has eyelid folds.  The embryo has a tail (which is actually part of the tailbone) which will disappear within the next few weeks.

  • Week 8Size of a raspberry (2/3”) – Baby is moving their arms and legs.  The fingers and toes are still webbed, but tail is almost gone.  Most of the major organs have now formed, and taste buds are beginning to form. Nerve cells in the brain are beginning to connect with one another.

  • Week 9Size of a grape – (7/8”) – No longer an embryo, your baby is now a fetus!!  Facial features beginning to develop, and baby now has earlobes.  Baby’s eyelids are now fused shut, and won’t open until about the third trimester. The heart beat is growing stronger!


  • Select a care provider (family doctor/OB/midwife), know what questions to ask!!

  • Start visualizing what type of birth you would like.  I recommend attending a Birth Art Circle!

  • Choose a prenatal vitamin. (Food-based tend to be easier to digest, and less likely to cause nausea.) Research the differences between folate and synthetic folic acid. (Broccoli, spinach, brussels sprouts, eggs, strawberries, lentils, beans, and asparagus are also great sources of folate!)

  • Ensure that you are getting proper nutrition. Keeping a diet log is a great way to ensure that you are getting plenty of food from each food group!

  • Start thinking about when you want to announce your pregnancy to friends, family, and your employer.

  • Many parents start taking weekly baby bump photos. You may not notice much difference at first, but it can be fun to look back at the end of your pregnancy and see how much your belly has grown!!