PREGNANCIES

One of the early serious plot lines revolved around the danger of pregnant women on the island. They all died before giving birth.  This was a serious story line, repeated twice in the show: first with Claire and her abduction, and second with Sun's "miracle" conception. (There is major flaw in the sideways arc that both women who gave birth in the island time-sphere gave birth to their daughters in the sideways after life.)

The reason why pregnant women died on the Island before they could successfully give birth was vaguely couched as an "infection." People, especially pregnant women, had to have shots in order to save themselves and their babies. But the cause was never explained. Ben kidnapped Juliet to have her investigate the island birth problem because she successfully got her infertile sister pregnant. Juliet was supposed to solve the problem, but did not. There was some aspect of the pregnancies that may have been tied to fetus "time skipping," but that was actually before the FDW was introduced as a deux machina device.

In Season 1 when Claire was pregnant with Aaron and got kidnapped and experimented on by Ethan, was a member of The Others who had a focus on children. They would later kidnap the tail section children.  Ethan was likely working with  Juliet to help Claire – he gave her injections, but those cause strange pyschotropic events in Claire's mind.  Claire was rescued Aaron was born on the island (something that was not supposed to happen). One explanation is that it was likely Aaron born on the Island without incident because Claire was already far enough along in her pregnancy before coming to the Island (just like Jacob and the Man In Black’s mother).

However, the pregnancy issue popped up again in Season 3 when Sun learned that she was pregnant (“The Glass Ballerina” & “D.O.C.” ) and was a the prominent focus of Juliet’s flashback arch (“One of Us“). If Sun conceived on the island, she was in mortal danger just like the dead Other women who could not come to term. One hard explanation was that Sun was pregnant before she arrived on the island, and that the baby was not Jin's. However, the baby problems occurred in island women in their third trimester, so both Claire and Sun would have been in danger. Another factor for Sun was that her daughter was born off the island which somehow saved the mother and child from the island's deadly "infection?"

One simple observation is that the motherhood drama was a story arc that fizzled out after Claire gave birth and Juliet was killed off.  It was filler drama because who is more at risk on a dangerous island than a pregnant woman?

However, in Desmond's island back story, we were told that everyone on the island was at risk. That Desmond had to take injections and not go outside because of the infection. We later learned that Kelvin was lying to Desmond. So it is possible that there was no island"infection," and that the pregnant women never came to term because of some other factor, such as poor prenatal care or individual risk factors (because at some point, there was a thriving community with Dharma, with children and a school).

One other explanation I had during the original series run was that pregnant women could not come to term on the island because the island was hell. In hell, sinners were not allowed to bring new life into a realm of punishment. A newborn has no sin to be punished so it would not be allowed to be born. And Ben, as a minion for Satan, was trying to get around that rule by finding a way to regenerate a new army for the devil himself (who could be the evil incarnate - - - smoke monster).

Likewise, there is a story problem with pregnant women in the sideways after life. If the sideways was purgatory or even a slice of heaven, why would dead women give birth to their already born children? That does not make any logical sense.

It would seem the infection of the island, whatever realm state it was, could have been a misstatement of some kind of dream-hallucination state that women with issues believed that they were pregnant and going to have a child. In the sideways world, in a similar vain, the reward for certain women was to give them what they dreamed about but did not achieve in the real human life: having a baby.

The fact that we never found out why pregnant women were dying on the Island still bugs a great deal of LOST fans. It is one of those sub-plots that was conveniently dropped but then later contradicted by other events.