Pregnancy Landmarks: When Can We Identify Them?
Pregnancy
Obie Editorial Team
What is a "pregnancy landmark"?
A "pregnancy landmark" is the earliest time in pregnancy when a pregnancy structure should be seen first. If iof not seen by that time, then there may be an issue that should be further evaluated. The following are typical pregnancy landmarks:
- Pregnancy test
- Gestational sac (GS) on ultrasound
- Yolk sac
- Crown-rump length (CRL)
- Fetal heartbeat is first seen
As pregnancy progresses you can make the pregnancy diagnoses seeing several landmarks where you would normally expect to see the pregnancy development. Pregnancy landmarks follow very clear rules and you would expect to identify them as the pregnancy progresses.
Below are the typical landmarks and when you would expect to see them:
| Landmark | Days Past Ovulation | Days after Last Period |
| Blood hCG >25 mIU/cc | 10 days | 24 days |
| Positive Urine HPT | 12-13 days | 26-27 days |
| 10 mm Gestational Sac on Sonogram Usually hCG above 2,500 mIU/cc |
21 days (3w+0d) | 35 days (5w+0d) |
| Yolk Sac/Embryo Usually hCG above 5,000 mIU/cc |
24 days (3w+3d) | 38 days (5w+3d) |
| Crown-Rump Length 4.5 mm | 28 days (4w+0d) | 42 days (6w+0d) |
| Fetal heartbeat is seen | 31 days (4w+3d) | 45 days (6w+3d) |
Usually, the fetal heartbeat is clearly seen by transvaginal sonogram by about 6 and 3 days after the first day of the last period if the cycle length was 28 days and ovulation happened around CD 14. That is 4 weeks and 3 days after ovulation/fertilization. In a woman with irregular and slightly longish cycles (say, 35 days versus a usual 28 days), the day of ovulation would actually be postponed to 1 week on top of the 14 days in the usual case, that is, she ovulates on Day 21.
