How many weeks early can a premature baby survive?

Written by Du Rui Xia
Obstetrics
Updated on June 05, 2025
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In clinical practice, infants born after 28 weeks but before 37 weeks of pregnancy are considered preterm. The survival rate of these babies varies; the earlier the birth, the lower the likelihood of survival. Clinically, babies born at 23 weeks have a 17% chance of survival; those born at 24 weeks have a 39% survival rate; at 25 weeks, the rate is 50%; at 26 weeks, it increases to 80%; and at 27 weeks, it rises to about 90%. Babies born between 28 and 31 weeks have an even higher survival rate, approximately 95%; and from 32 to 33 weeks, the survival chances are comparable to those of full-term babies. Records indicate that the earliest preterm baby to survive was born at 21 weeks and five days, in Canada.

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Written by Zhao Li Li
Obstetrics
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Causes of Premature Birth

Generally, there are many reasons that can cause symptoms of preterm birth. Normally, due to reasons such as cervical dilation, or the occurrence of regular abdominal pain, preterm labor may be induced. In some cases, long-term vaginal inflammatory conditions can lead to premature rupture of membranes, or cervical canal dilation may also cause preterm birth. If symptoms of preterm birth occur at present, it is necessary to actively suppress contractions, protect the fetus, and provide symptomatic treatment. If this is ineffective, it is advisable to actively prepare for rescuing and caring for the newborn.

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Written by Liu Wei Jie
Obstetrics
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Is a posterior placenta more likely to lead to premature birth?

The placenta is divided into anterior and posterior walls, with the posterior wall being a normal location for the placenta, which is unrelated [to preterm birth]. Generally, there is a hereditary tendency for preterm birth, and it is more likely to occur in individuals with certain physical constitutions or in cases of twin pregnancies. Additionally, people with gestational diabetes are also prone to preterm birth. Therefore, the posterior wall of the placenta has no correlation with preterm birth. Conditions like placenta previa or premature placental detachment are placental positions that can lead to preterm birth issues, and some people may experience preterm birth under these circumstances.

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Written by Zhang Lu
Obstetrics
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How is premature birth defined?

Preterm birth is defined in relation to miscarriage and full-term birth. A birth before 28 weeks of pregnancy is considered a miscarriage; a birth after 37 weeks of pregnancy is considered full-term; and a birth between 28 weeks and 36 weeks and six days is considered preterm. Since preterm birth occurs in the late stages of pregnancy, the fetus has a certain chance of survival. However, efforts should be made to delay the timing of preterm birth as much as possible to increase the survival rate of the fetus. It is generally believed that births between 28 and 34 weeks are considered early preterm, during which the survival probability of the fetus is relatively low; whereas births after 34 weeks up to 36 weeks and six days are considered late preterm, during which the maturity of the fetus is higher and the survival rate is also relatively high.

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Written by Zhao Li Li
Obstetrics
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Is it normal for a premature baby to weigh more than five jin?

If the newborn is currently premature and weighs a bit over five jin (approximately 2.5 kilograms), it is generally considered within the normal range. Typically, if a newborn weighs more than 2500 grams, it is considered a full-term birth weight and there are no abnormalities. Therefore, if the newborn's weight is within the normal range after birth and there are no abnormalities in the development of the organs, it is possible to observe temporarily without the need for an incubator. It is also crucial to closely monitor the various vital signs of the newborn and pay attention to normal feeding and care.

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Written by Zhang Lu
Obstetrics
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What are the symptoms of premature birth?

Premature birth refers to delivery occurring between 28 and 36+6 weeks of pregnancy. The symptoms of premature birth primarily include the following aspects: First, regular uterine contractions occur. These contractions can lead to the descent of the fetal head and exert pressure on the cervix, which is necessary for the delivery of the fetus. It generally manifests as pain every three to five minutes, with each episode of pain lasting more than one minute, and both the frequency and intensity of the pain gradually increasing. Second, the appearance of "bloody show" occurs. As the fetus descends, it can cause the rupture of capillaries at the edge of the membranes, leading to bloody show. Third, there is a noticeable feeling of heaviness or pressure. Gynecological examinations can reveal dilation of the cervix and shortening of the cervical canal. When these symptoms appear, an assessment for premature birth should be conducted, and preparations for premature delivery should be made.