Is it normal for the placenta to be 3 cm from the cervical opening?

Nov 14, 2025 Source: Cainiu Health

Dr. Zhang Lu

Introduction

If the gestational age is less than 28 weeks at the time of examination, the lower uterine segment has not fully formed and the placenta may appear relatively low, with a distance of 3 cm from the internal cervical os, which is a common presentation of placenta previa. As gestational age increases, the uterine body gradually enlarges and pulls upward, causing the placenta to typically migrate upwards as well. By 28 weeks of gestation or later, the placenta may return to a normal position. In such cases, there is no need for excessive concern; regular follow-up examinations are sufficient.

Under normal circumstances, if the placenta is 3 cm away from the cervical opening before 28 weeks of gestation, it may move upward with uterine growth and reach a normal position as pregnancy progresses. However, if the placenta remains 3 cm from the cervix after 28 weeks, it is considered low-lying placenta, and there is an increased risk of bleeding. Medical consultation is recommended if there are any concerns. Detailed analysis is as follows:

If the gestational age at detection is before 28 weeks, the lower uterine segment has not fully formed, so the placenta may appear relatively low. A distance of 3 cm from the cervical opening is commonly seen in cases of placenta previa during early pregnancy. As gestational age increases, the uterine fundus gradually enlarges and pulls the placenta upward, allowing it to typically migrate to a normal position (≥2 cm from the cervical opening) by after 28 weeks. In such cases, excessive concern is unnecessary; regular follow-up examinations are sufficient.

If the gestational age at detection is beyond 28 weeks and the placenta remains 3 cm from the cervical opening—failing to meet the normal distance criteria—it is classified as low-lying placenta. By this stage, the lower uterine segment has largely formed, making the placental position relatively fixed with limited chance of upward migration. During the remainder of pregnancy, painless vaginal bleeding may occur due to uterine contractions or external stimuli, which in severe cases could compromise maternal and fetal safety. Close monitoring of physical condition is therefore required.

Upon discovering that the placenta is 3 cm from the cervical opening during prenatal screening, the gestational week should be recorded and regular ultrasound follow-ups scheduled as advised by a physician to monitor changes in placental position. Immediate medical attention is necessary if symptoms such as vaginal bleeding or abdominal pain occur, to ensure maternal and fetal safety.

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What causes slight bleeding in the third trimester of pregnancy without abdominal pain, and what should be done?

In late pregnancy, slight bleeding without abdominal pain may be caused by factors such as bloody show, cervical polyps, placenta previa, early placental abruption, or vaginitis. Symptoms can be managed through symptom observation, bed rest, medication, and medical monitoring. If bleeding increases or abdominal pain occurs, immediate medical attention is required. In late pregnancy, the cervix matures, and the fetal membranes near the internal cervical os may separate from the uterine wall.

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At what time of day is the HCG level highest?

From the perspective of HCG secretion mechanism, it is continuously secreted by placental trophoblastic cells, and the secretion process is relatively stable, without significant peak variations according to circadian rhythms as seen with certain other hormones. During daytime, when the body is active and metabolism functions normally, HCG levels remain relatively stable, with minimal variation in test results at different times, making it difficult to identify a single peak time.

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Why are there so few people with a posterior placenta?

It is not uncommon for embryos to implant on the posterior wall of the uterus; it is simply slightly less common compared to anterior wall implantation. The main reasons include anatomical features of the uterus, the random nature of embryo implantation, pelvic environmental factors, hormonal regulation, and history of prior uterine procedures. Both posterior and anterior wall implantations are considered normal. If abnormal symptoms such as abdominal pain or vaginal bleeding occur during pregnancy, prompt medical attention is recommended.

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Why does the stomach become hard after slight movement at 27 weeks of pregnancy, and what should be done?

In general, during the 27th week of pregnancy, slight physical activity causing the abdomen to feel hard may be due to false labor contractions (Braxton Hicks contractions), uterine enlargement stretching ligaments, preterm labor signs, placental abruption, or red degeneration of uterine fibroids. Depending on the specific situation, improvements can be achieved through general management, medication, or surgical treatment. Pregnant women should avoid strenuous exercise and walk within their limits. Regular prenatal checkups are essential to monitor uterine and fetal conditions.