Pregnancy week 4 - baby's development and your body
The information in this article is intended for general information only and does not replace medical advice. Always contact your midwife or maternity care provider if you are concerned about your or your baby’s health.
Are you in week 4 of your pregnancy? Learn all about how the embryo develops this week, changes in your body, and early pregnancy symptoms.
Week 4 is the second week after fertilization.
The fertilized egg continues to divide and grows rapidly. At the beginning of this week, the fertilized egg reaches the uterus and attaches itself there, if it hasn't already done so.
Size:
The embryo is about 0.1–0.2 cm or 0.039–0.079 inches in size, from head to rump.
Weight:
Less than 1 gram.
Embryo development:
The rapidly growing ball of cells, also called a blastocyst, is now embedding itself into the uterine lining. The cells continue to divide and also separate into two parts: one that will become the embryo and one that will become the placenta.
Between them, a structure called the connecting stalk is formed, which will eventually become the umbilical cord. The placenta and your baby will be genetically identical.
Your body:
It’s still very early, so noticeable pregnancy symptoms are uncommon this week. However, some may observe slight changes in their usual post-ovulation symptoms.
Certain highly sensitive pregnancy tests may even show a positive result by the middle of this week.
1. 1177 Vårrdguiden (Sweden's national online healthcare portal). “Pregnancy week by week”, https://www.1177.se/barn--gravid/graviditet/om-graviditeten/graviditeten-vecka-for-vecka/
2. Cleveland Clinic. Fetal development: Stages of growth, https://my.clevelandclinic.org/health/articles/7247-fetal-development-stages-of-growth
3. Mayo Clinic. Prenatal care: Healthy pregnancy week by week, https://www.mayoclinic.org/healthy-lifestyle/pregnancy-week-by-week/in-depth/prenatal-care/art-20045302