The answer to this question is not simple. The student may be permitted by the Designated School Official to enroll for less than full-time where it is recommended for academic reasons or due to the student’s illness [I guess a complicated pregnancy qualifies]. The regulations are not specific as to how long a student may take less than a full-time load. An F-1 student is considered to be in status during the school’s annual vacation, if the student is eligible for and intends to resume full-time studies in the next term.