First, I am sorry you had to go through 2 rounds of requests for more evidence (RFE). That, in itself, is unusual and without being disparaging, indicates to me that the original L1 extension application was woefully incomplete.
Second, if you are denied there is no grace period. You must leave the country immediately or you will be out of status. If you remain out of status in excess of 180 days you will be banned from entering the U.S. for ten years. Your status expired about 5 months ago.
Third, get a good immigration lawyer. He or she may be able to get relief under the family unity act. Many international airlines will not allow woman to fly whose pregnancies are considered imminent (there is debate as to what time frame "imminent" refers to).
This issue should be addressed immediately. Do not wait until you get a rejection.
Finally, it will not affect your baby's status, per se. If the baby is born in the U.S. it is a U.S. citizen, regardless of the status (lawful, unlawful, out of status) of the parents. If the baby is born abroad to non u.s. citizen parents then the baby will have to apply for a visa just like everyone else.
This answer is for information purposes only and does not constitute legal advice nor establish an attorney client relationship.