Early Fetal Development Week by Week
- As a result of sexual intercourse, the fertilized egg becomes an embryo within six to 12 days after conception. Hormones called progesterone are produced by the body to prepare and protect the uterine lining, which will act as the cradle for the developing embryo.
- When the pregnancy reaches its fifth week, the embryo eases into its third week of development. This is the period in which an ultrasound screening can show the gestational sac. Sometimes, this sac is shown in the scan even before the embryo is visibly detected. Then at the start of the sixth week, a yolk sac begins to take shape inside the gestational sac. The developing fetus will get its nourishment from the yolk sac.
- A fetal heartbeat begins to show in the ultrasound scanning when the embryo reaches its fourth week. Afterwards, a more recognizable fetal pole starts to take shape. It is the length from the embryo's head to the end, which resembles a tail. If there is no fetal pole or heartbeat detected, the doctor can do another ultrasound scan within three to seven days.
- With a stronger heartbeat detected in its fifth week, the embryo continues its development. During this period, doctors monitor any risks of miscarriage or ectopic pregnancy by carefully measuring the gestational sac and fetal pole. If the sac is less than 16 to 18 millimeters with no fetal pole, or if there is no heartbeat from a fetal pole measuring five millimeters, it is likely that a miscarriage has occurred. To rule out ectopic pregnancy, repeated scanning and further tests are done in the following three to five days.
- When pregnancy reaches the eighth to ninth week, the seven-week old embryo grows into a fetus with organs slowly developing along with it. Fetal movement can also be seen through the ultrasound scan. The heartbeat is also much stronger, at a normal rate of 140 to 170 beats per minute. The physician will monitor the fetal heartbeat closely to make sure the pregnancy continues in its normal development.