بسم الله الرحمن الرحيم

The pregnant divorcee or widow has an iddah (specific time period before she can get married which is) until she has given birth, due to His statement:

And for those who are pregnant (whether they are divorced or their husbands are dead), their ‘Iddah (prescribed period) is until they deliver (their burdens)
Soorah Al-Talaaq Verse 4

(So) the marriage contract with her is obsolete and the marriage is not complete.

Fataawa Al-Lajnah Ad-Daa’imah 4945