The Gemora states that a child born in its eighth month will not survive. In today’s day and age, that does not seem to be the case. How are we to understand this?
Rabbi Gil Student wrote an essay regarding the halachic responses to scientific development. Here is an excerpt from his discussion. (It can be found in its entirety here:
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As we already mentioned, the Talmud claims that babies born in their eighth month from conception are not viable. The Chazon Ish (Yoreh Deah 155:4) explains that the sages observed that babies born in their seventh month rarely survived. However, a small but significant percentage lived. In the eighth month, the survival rate dropped even lower. But in the ninth month, the survival rate rose sharply. This phenomenon is reflected in other ancient medical works such as those by Hippocrates and Galen (see J. Preuss, Biblical and Talmudic Medicine, 14:14). Keep in mind that until recently infant mortality was very high. Many newborns never lived past their first month. Indeed, this is reflected in halacha in that parents do not fully mourn a baby that dies in its first month alive. Before the month passed, there was a strong likelihood that the baby would not survive.
To explain this drop in infant survival in the eighth month, the sages adopted the medical explanation that babies develop along two paths - a seven month path and a nine-month path. Babies in the seven-month path progress at a rate so that they are fully developed after seven months while babies in the nine-month path are only fully developed after nine months. A nine-month baby born in its seventh or eighth month cannot survive because it is not sufficiently developed. However, the rabbis observed that there were still some very few babies born in their eighth month who survived. These babies, it was explained, were seven-month babies who were born late.
With all this in mind, we can understand the following from Tosefta Shabbat 16:4.
Who is an eight-month [baby]? Any [baby] who has not completed his months. Rebbe says: His signs identify him - his hair and fingernails... Rabban Shimon ben Gamliel says: Whoever has lasted thirty days is not a stillborn...
According to the first anonymous opinion, any baby born in its eighth month, i.e. who has not completed its nine-month development period, is considered to be an eight-month baby that will not survive. According to Rebbe, only a baby that is born in its eighth month and is not developed enough to have fingernails and hair is considered to be an eight-month baby. Even if a baby is born in its eighth month, if it is fully developed it is deemed viable and treated appropriately. According to R' Shimon ben Gamliel, any baby that survives its first thirty days is deemed viable. In Shabbat 136a, Shmuel rules like R' Shimon ben Gamliel. Whether R' Shimon ben Gamliel is coming to add to Rebbe's criteria, so that even a partially developed eight-month baby is deemed viable if it survives thirty days, or he is coming to subtract from Rebbe's criteria, or a number of other possibilities is discussed by the commentaries. For summaries of these discussions see R' Aharon Yaffen's footnotes to Mossad HaRav Kook's edition of the Ritva on Yevamot 80b and Minchat Yitzchak 4:123:3. Regardless, the Shulchan Aruch (Orach Chaim 330:7-8, Yoreh Deah 266:11) rules that a baby born in its eighth month that has fingernails and hair is considered viable in regard to the laws of Shabbat. What is significant is that the rabbis recognized that a baby born in its eighth month can live a full and long life. However, based on their observations and medical knowledge, they said that the overwhelming majority does not.
Halachic Ramifications
The non-viability of an eight-month baby has halachic ramifications. A widow whose only child is a non-viable eight-month baby is considered childless in regard to the levirate marriage. If she had given birth to a viable child she would not be obligated to perform the levirate marriage or chalitzah ceremony. However, since her child's chances of living are so remote she is considered childless and is prohibited from remarrying until she fulfills the necessary biblical requirements (Yevamot 80a-b).
Additionally, the needs of a seriously ill person may be cared for even if they require violating the laws of Shabbat. A newborn baby, in particular, requires great care. While most of those needs do not require violating Shabbat, if they did Shabbat could be violated. However, for a non-viable baby that has essentially no chance of survival, Shabbat may not be violated. The concerns of an eight-month baby that does not have fully grown fingernails and hair do not override Shabbat (Shabbat 136a).
Today, modern science gives us a different understanding of a fetus' development than that of the sages. Babies develop steadily until their last month. Those born in their seventh month are less likely to survive than those born in their eighth month. Premature babies can suffer from difficulty in modulating temperature and underdeveloped capillaries and lungs which can be alleviated with respirators and incubators. Today, babies born in their eighth month routinely survive. How should halacha respond to this change?
Defining an Eight-Month Baby
Before we address this question, let us first discuss an often overlooked issue - a definition of terms.
What is an eight-month baby?
The Talmud says that a normal (nine-month) gestation period is approximately 271 days from conception. Modern medicine places the due date of a baby at approximately 280 days from the mother's last menstrual cycle. Since a religious woman may only have marital relations beginning with 12 days after starting to menstruate (after she immerses in a mikva), the 271 days translate into approximately 283 days, which is essentially equal to modern medicine's 280.
Modern medicine divides the 280 days into ten months of 28 days. What is generally called the ninth and final month is really the tenth month - from weeks 36 to 40. The eighth month is from weeks 32 to 36 and the seventh month is from weeks 28 to 32.
Halacha divides the 271 days into nine months of about 30 days each (Responsa Rashbash 513). Translating that into the weeks we used above (from the last menstruation), the ninth month is from weeks 35.7 to 40. The eighth month is from weeks 31.4 to 35.7 and the seventh month is from 27.1 to 31.4.
Additionally, the simple understanding of the Talmud is that an eight-month baby is one born after eight full months, i.e. after 35.7 weeks. This is the understanding of most commentators with only the Ramban dissenting (Responsa Rivash 446).
It is a daily occurrence for babies to be born at 36 weeks and survive without the assistance of respirators or incubators. With their assistance, the survival rate is greater than 95%. How should the halachic community react to this undeniable reality?
The first point that needs to be made is that halacha only needs to address those babies born without fully grown fingernails and hair. Only those born between 35.7 and 40 weeks who are under-developed are an issue. Never the less, the problem remains.
2b. Nature Changed
The Rashbash (R' Shlomo ben Shimon Duran; early 15th century) quotes the authors of Tosafot as saying that already by their time nature had changed. While in the days of the Talmud babies' months were determined by how many months had been completed, they are now calculated by which month the baby is in. While for the Talmud a baby born in weeks 35.7 to 40 (after eight months) was premature, this baby would now be considered full-term (a nine-month baby). Now, only babies born in weeks 31.4 to 35.7 (in their eighth month) are considered premature (Responsa Rashbash 513). This is how the Rama ruled in Shulchan Aruch (Even HaEzer 156:4). The Chazon Ish (Yoreh Deah 155:4) continued along this line and noted that today a significant number of babies born in their eighth month are viable on their own. This must mean that nature has changed, although he does not speculate as to whether it is due to better prenatal care, healthier diets, or other causes. Since nature has changed and eight-month babies are no longer inherently at risk, the halacha as it relates to current nature is different than it is in regard to talmudic nature. Since eight-month babies are deemed viable, Shabbat may be violated for their needs and women who give birth to such a baby are not considered childless.
There were two issues that we pointed out above. One is that babies born after eight months are not only viable but are more viable than those born after seventh months. The other is that with modern medical care even premature babies can survive. The Chazon Ish solved both issues by ruling that nature has changed and that eight-month babies are no longer born non-viable. Any baby that can survive, whether on its own or with medical help, is considered a viable baby.
Alternate Solution
The Minchat Yitzchak (4:123:19-20) refused to go that far. He was not ready to say that the talmudic understanding of the development of babies is no longer true. Of the two issues above, he only addressed the second. Even though eight-month babies are inherently less viable than others, modern medical care can help those babies survive. Since these babies become viable through medical assistance they are therefore viable. It is not that nature has changed. Rather, modern medicine has found techniques to help the non-viable survive.