Does the presence of yolk sac necessarily mean there will be a fetal heartbeat or fetal bud? When can the yolk sac be seen?

We all know that after a period of time in early pregnancy, the fetus will slowly develop a fetal heartbeat and a fetal bud, which can be seen through B-ultrasound. In fact, before the fetal heartbeat and fetal bud appear, there will also be a gestational sac and a yolk sac. The yolk sac still has a certain effect on the fetal heartbeat and fetal bud.

Does the presence of yolk sac necessarily mean there will be a fetal heartbeat and fetal bud?

If the quality of the yolk sac is poor, there is still a chance of an empty sac, and even if a fetal bud appears, there may not be a fetal heartbeat. However, this is based on the fact that the expectant mother's menstrual cycle is relatively regular. If the menstrual cycle is irregular and the fertilized egg implants late, the time for the fetal heartbeat and fetal bud to appear will be delayed.

Generally, the yolk sac can be observed around 5 weeks, and the embryo and fetal heart can be seen at 6 weeks. The yolk sac is a bright circle inside the gestational sac. The normal diameter of the yolk sac is 3 to 10 mm.

The fetal heartbeat is more accurately called the primitive heart tube beat, and it appears after the embryo. The appearance of the embryo and the fetal heartbeat indicates the survival of the embryo. After the embryo and the fetal heartbeat are found, if there are no special circumstances, the NT examination can be performed at 11 to 13+7 weeks.

When can the yolk sac be seen?

The yolk sac is formed at around 3 weeks of pregnancy and can be seen at around 6 weeks of pregnancy. Before the placenta is formed, it mainly provides nutrition and blood to the fetus. At around 6 weeks of pregnancy, the placenta is formed and a fetal bud grows in the yolk sac. At around 8 weeks of pregnancy, primitive fetal heartbeats appear. Until around 12 weeks of pregnancy, the embryo differentiation is completed, the yolk sac completes its task and gradually atrophies.

The presence of a yolk sac does not necessarily mean the presence of an embryonic bud, but without a yolk sac, the embryo will definitely not develop into an embryonic bud in the later stage.

What is the yolk sac?

After the embryo undergoes body folds at about 5 weeks of gestation, the archenteron will split into two, one part becoming the archenteron inside the embryo, and the other part becoming the yolk sac outside the embryo. As the embryo slowly develops various organs of the fetal body, the yolk sac will be slowly consumed and atrophied, until it slowly disappears at 12 weeks of gestation and becomes a part of the embryo. It is no exaggeration to say that the yolk sac is the hematopoietic field in the process of embryo forming fetus.

Generally speaking, the gestational sac and yolk sac can be seen on the 35th day of pregnancy. The embryonic bud is formed around the 40th to 50th day. The embryonic heart appears on the 50th to 60th day. If the menstrual period is delayed, it means that the appearance of the yolk sac, embryonic bud and embryonic heart will also be delayed.