One of the first things that doctors look at when a woman finds out she is pregnant is the size of the fetal egg. The embryo starts to develop in this tiny sac, and its development can reveal crucial information about how the pregnancy is going.
Ultrasound can be used to measure the size of the fetal egg during the first few weeks of pregnancy. Standard growth charts are compared with these measurements to make sure everything is progressing as planned. Keeping track of the fetal egg’s dimensions can provide parents and doctors with peace of mind, even though every pregnancy is unique.
We’ve created a table below that breaks down the average fetal egg size by week. You can learn more about what to anticipate at each stage of the early pregnancy process by using this guide.
- How and why measure measurements?
- How the dimensions are changing?
- Reasons for deviations
- Hypoplasia
- Hydatidiform mole
- Anembryony
- Too large an egg
- Video on the topic
- When the fertilized egg is visible, but the embryo is not
- Ultrasound signs of pregnancy 5-6 weeks 2025 05 03 14 31 32
- Sizes of the fertilized egg by weeks of pregnancy in the table
How and why measure measurements?
The fetal egg completes the formation by the third week from the day of conception, it is by this time that it can already be seen at the ultrasound (this is about a week of delay of menstruation). It consists of an embryo itself, shells, chorion, amnion and yellow bag. The chorion is responsible for the attachment of the embryo to the wall of the uterus and nutrition, for the production of hormones necessary for the continuation of pregnancy. Amnion forms the aquatic environment (amniotic waters), the yolk bag is a food supply, and inside the fetal egg your unborn child looks like a thin strip. The detection of the fetal egg in the uterine cavity against the backdrop of menstruation delay is a reliable sign of pregnancy, but at the very early stages the doctor will not be able to clarify anything more. The fact is that there can be two germs in one egg (twins), and this will become noticeably much later. Sometimes the fetal egg turns out to be empty, that is, it does not have an embryo, and in the early stages this is also not visible.
The fetal egg sizes are measured in order to ascertain the gestational age and to evaluate the accuracy of the early stages of embryonic development.
How the dimensions are changing?
Until 8 weeks of pregnancy, doctors almost have no way to understand, but how, in fact, the crumb itself grows and develops, because its size is very small. Measuring individual body parts is technically impossible, and here the size of the fertilized egg comes to the rescue. It grows in accordance with certain obstetric terms, and this indicator is very similar in different children at the beginning of pregnancy. It is later that children become large and miniature, with large heads or small hands, in a word, the way nature intended them to be. And during the period of embryogenesis, while organs and tissues are actively forming, the growth rate is approximately the same for everyone. That is why the size of the ovum and the dynamics of its growth are important indicators for clarifying the term. Speaking about the size of the ovum, they mean one size – it is called the SID (average internal diameter). It is a segment laid by a somnologist between the walls of the egg so that its ends are on opposite sides. At the first ultrasound, which a woman may visit at 5-6 weeks, the SID will be the only value that the doctor can determine accurately. A little later, another size will be determined – the coccygeal-parietal or CTE (the distance from the coccyx to the crown of the embryo).
Values like the ovum’s area and volume are not very important from a diagnostic standpoint, but they are frequently measured nonetheless because the ultrasound scanner’s software allows for it.
Table of normative values of SVD, CTE and other indicators
| Term in weeks | SVD, mm | CTE, mm | Area, mm^2 | Volume, mm^3 |
| 5 | 5–17 | 1–2 | 245 | 2187 |
| 6 | 13–21 | 4–5 | 363 | 3943 |
| 7 | 21–23 | 5–16 | 432 | 6912 |
| 8 | 29–31 | 10–24 | 675 | 13490 |
| 9 | 33–35 | 16–37 | 972 | 16380 |
| 10 | 39–43 | 24–48 | 1210 | 31870 |
| 11 | 47–56 | 34–59 | 1728 | 55290 |
| 12 | 56–58 | 42–73 | 2350 | 87080 |
| 13 | 63–66 | 51–87 | 3072 | 131070 |
If the results of your ultrasound show that the size of the ovum is only slightly different from the norm, you shouldn’t freak out or worry. If ovulation was late, implantation happened later than 7-8 days after ovulation, and large sizes suggest that ovulation happened earlier or that implantation happened early, then individual fluctuations in the smaller direction are quite possible.
Only notable deviations (more than 30% from the norm) should be taken seriously; in this instance, doctors will undoubtedly look into why the ovum’s size does not match the norm for the weeks of pregnancy.
Reasons for deviations
Women who have been waiting a long time to become pregnant tend to be very suspicious and can get upset or worried about anything. In particular, the doctor may utilize cryptic and esoteric terminology to gauge the ovum’s size. For instance, the term "deformed" has certain connotations. You shouldn’t be concerned because the uterine muscles’ increased tone causes the egg to be deformed in 90% of cases.
The egg’s outlines will be accurate if the tone is eliminated. Stated differently, deformation is not a disease. Among the potential issues, the following need to be mentioned.
Hypoplasia
The membranes do not grow as quickly as the embryo. The coccygeal-parietal size in this instance is greater than the period norm, while the SVD is below the norm, indicating a discrepancy between the SVD and CTE. This could be the result of an infection, an imbalance in hormones, or abnormalities in the embryo. The cause is frequently still unknown.
The embryo dies in the vast majority of cases, and the prognosis is not good. A pregnancy that is frozen occurs. A spontaneous miscarriage that occurs prior to the embryo’s death is the second possibility. There is no improvement and the pregnancy continues despite the ovum’s hypoplasia.
Hydatidiform mole
An embryo does not exist. All that is present are the chorion’s overgrown membranes, which have formed numerous bubble-cysts. With ultrasonography, they can be accurately diagnosed and resemble grapes. The cause is a subpar egg cell that was unable to supply enough DNA for this process when it merged with the male reproductive cell. Dad’s chromosomes just double, so even in a partially formed embryo, it cannot grow and develop. When a woman’s hCG level is noticeably higher than average, she may mistakenly believe that she is carrying twins or triplets.
A hydatidiform mole in one out of every five women progresses to chorioepithelioma, a malignant tumor that is prone to fast and aggressive metastases. As a result, it’s critical to get rid of the mole as soon as it’s discovered.
Anembryony
There is a fertilized egg present and growing, but no embryo. It takes 6-7 weeks to notice this, at which point it’s time to record the heartbeat and CTE. None exist. Genetic errors, acute infections, radiation exposure, and other factors—not all of which have been thoroughly investigated—are frequently the causes.
It is crucial to carry out a dynamic analysis. Curette the uterine cavity or use vacuum aspiration if the embryo is not found within a few days or a week.
Too large an egg
Pathologies of the fetus and pregnancy may occasionally be indicated by a notable excess in the size of the fertilized egg. A fetal heart rate violation and a drop in CTE are frequently observed in large eggs. In this instance, the physician might believe that these symptoms are precursors to fetal developmental arrest.
A blood test for hCG is recommended if the excess size is noted early on (for instance, at 6 weeks). It is plausible that one egg is harboring two monochorionic twins. In order to measure each embryo, a second ultrasound is required in a few weeks if the blood results support this.
| Week of Pregnancy | Size of the Fetal Egg (mm) |
| 4 weeks | 2-3 mm |
| 5 weeks | 5-6 mm |
| 6 weeks | 12-16 mm |
| 7 weeks | 18-24 mm |
| 8 weeks | 25-30 mm |
| 9 weeks | 32-40 mm |
Throughout pregnancy, measuring the size of the fetal egg can help doctors and expectant parents keep an eye on the developing baby. Even though every pregnancy is different, knowing roughly how the fetal egg develops every week gives comfort in knowing that everything is going according to plan.
The fetal egg dimensions by week table provides an easy-to-understand method of visualizing this growth. This feature allows you to compare your results with typical development patterns by displaying the expected size ranges for each week.
It’s crucial to keep in mind that minor variances are typical and that growth might vary somewhat between pregnancies. You shouldn’t be too concerned if your doctor is unconcerned. Frequent examinations will give you more specific information about your baby’s health.
One of the first markers of pregnancy development is the size of the fetal egg, which offers important details about the health and development of the unborn child during the first trimester. This article helps expectant parents understand what to expect as their baby grows by providing an easy-to-read table that shows the typical dimensions of the fetal egg for each week of pregnancy.
