3 Weeks Pregnant - Weekly Pregnancy Symptoms

The Fertilized Egg Implants in your Uterus During Week 3—
You Have Conceived!

265 DAYS TO GO. . .


Breast Pain
51% of women experience breast pain and tenderness as a symptom during week 3 of pregnancy. More >>
51% of women experience fatigue as a symptom during week 3 of pregnancy. More >>
46% of women experience cramping as a symptom during week 3 of pregnancy. More >>

The miracle of life begins. The 23 chromosomes of your partner’s sperm, and the 23 chromosomes of your egg have combined to create the zygote, which forms when a fertilized egg starts its first few cell divisions. Fertilization is now complete, and your own hormones naturally stop your next menstrual cycle from occurring. The newly fertilized embryo triggers your pituitary gland to release hormones responsible for stopping your menstrual cycle.

Pregnancy 3 weeks pregnant fertilization


Fertilization occurs once the sperm swim up the fallopian tube and meets the egg. The sperm carries genetic information and enzymes that help it penetrate into the egg.

The Blastocyst forms as the cells inside the egg rapidly divide. By the end of the week the blastocyst will reach the uterus where the outer lining of cells anchor to the uterine wall. The cell cluster inside the blastocyst creates the beginnings of the embryo.

Week 3 baby embryo size poppy seed
Embryo Size
Your baby is about the size of a poppy seed during week 3.

LENGTH: 0.03 in / 0.08 cm
WEIGHT: 0.002 oz / 0.06 g

View Weekly Growth Chart >>
Congratulations, you are pregnant! This new hormone your pituitary gland produces is called human chorionic gonadotrophin, or hCG. This hormone stops your menstrual cycle, and maintains the high levels of the hormone progesterone, which is vital for your pregnancy. The fertilized zygote has reached the uterus, but is not yet implanted in the uterine wall. As cell division occurs, the larger cluster of cells that has developed is now called the blastocyst. The blastocyst spends several days within the uterus before implanting itself within the uterine wall.

The blastocyst is preparing to implant itself in the uterine wall, and its placenta will start to form. At about day 7 after fertilization, the blastocyst makes room to implant itself in the lining of your uterus by eroding cells to sink beneath the surface. The blastocyst secretes hormones which stimulate the uterus to support the pregnancy rather than shed its lining. From this point, the innermost cell layer will form the placenta and amniotic sac which will enclose the embryo.

As cell divisions are occurring, the possibility of twins may cross your mind. Two separate eggs may have been released and fertilized, which results in fraternal twins. If one egg has been fertilized and splits into two embryos, then identical twins are formed. The timing of the split is crucial in the formation of the placentas and amniotic sacs. If the zygote splits in the first 3 days, then two placentas and two amniotic sacs develop within the uterus. If the split occurs 4-9 days prior to fertilization, or in the blastocyst stage, the babies will share a placenta but have separate amniotic sacs. If the split occurs after day 9, the babies will share a placenta and an amniotic sac.

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