Tucson Women’s Center is unique in its approach to reproductive health. We offer services to women who intend to carry their pregnancy to term, women who wish to end their pregnancies, and women who are undecided. No matter which group you are in, understanding fetal development is important.

Women who plan to carry to term are always interested to explore the progress of fetal development. For women considering abortion, fetal development can also be very important in establishing when or if to terminate. It is for these reasons that TWC is currently developing educational materials that discuss fetal development at various stages of pregnancy. For now, we would like to briefly touch on issues of fetal development in the first trimester. This discussion is geared more towards women who have NOT made a decision on whether to continue their pregnancy to term.

Women who are considering termination generally have questions that fall into 3 main categories: 1) Is there a heartbeat? 2) What is the actual size of the fetus? 3) To what extent are the various organ systems developed?


THE HEARTBEAT

Because of technical advances, the answer to the question of when a heartbeat can be seen has changed over the years. When women asked this question 20 years ago, the answer was 9-10 menstrual weeks*. Now the answer is closer to 6-7 weeks. Who knows what the answer will be 20 years from now? For women who are factoring in the presence of a heartbeat into their thinking, it is important to note the changing status of our technology and how it might impact the answer to this question now and in the future.


FETAL SIZE

From the medical standpoint, measuring the size of the pregnancy is done in order to estimate gestational age (or more commonly, how far along). From the patient perspective, measuring the pregnancy helps to complete the mental picture of what is going on. The methods used to measure the fetus become increasingly more elaborate as the pregnancy progresses. In the first trimester, the measurements used are:

• Gestational sac size (GS) which is a measure of the sac in which the fetus resides. This measurement is most often used between 4-6 weeks
• Crown-rump length (CRL) which is essentially an end to end measurement of the fetus. As development progresses, it is the distance from the top of the fetal head to the “rump” (excluding lower limb development). This measurement is most often used from 6-12 weeks
• The biparietal diameter (BPD) which is a side to side measurement of the fetal head. This measurement is most often used between 12-14 weeks.

It is important that you learn to speak the same language of your provider when discussing fetal size to avoid misinformation. The chart below contains fetal sizes using these three types of measurements.

ORGANOGENESIS

This term refers to the process by which organs develop. A full discussion of this topic is beyond the scope of this essay, but there is one landmark worth noting. Most medical practitioners believe that organogenesis is completed in the 12th week. That means that the fetus at twelve weeks is essentially similar to a term infant, but in miniature.

One of the topics that arise during a discussion like this is whether the fetus has developed to a point that it feels pain. For every person that believes that the fetus does not feel pain, there is someone who believes that it does. For that reason, it is the position of TWC that this question can not be answered with certainty.

We hope that you have found this essay helpful and we encourage you to contact a staff member if you have any other questions.

* The medical community uses menstrual weeks when discussing the length of pregnancy. For example, If the first day of your last menstrual period was January 1st, and you had intercourse on January the 14th and became pregnant, then on February the 1st, you are 4 weeks (and a few days) pregnant, NOT 2 weeks pregnant. Providers use this system because most women remember when they had a period but do not always know exactly when they conceived.