2 premature babies...likeliness of having the 3rd premature?

Looking for some insight of moms of preemies! My first little girl was born 36 weeks and did fairly well after birth, no complications or breathing treatments needed. My second daughter was born at 33 weeks 1 day despite our efforts in using makena - progesterone injections. I'm now 20 weeks with our first little boy and I am trying the makena again. What are the chances of this little guy being born early as well? My OB seems fairly certain he will come early too being all my others were. Have any of you had 2 preemies and your last closer to full term?