Final answer:
Submucosal fibroids are the most likely to cause subfertility or early pregnancy losses, due to their location beneath the uterine lining and potential to disrupt the uterine cavity.
Step-by-step explanation:
The type of fibroid most likely to cause subfertility or early pregnancy losses is the submucosal fibroid. Submucosal fibroids are located beneath the lining of the uterus and can distort the uterine cavity, which may interfere with the implantation of the embryo or the development of the placenta. Other types, such as intramural (within the muscle wall of the uterus), subserosal (on the outer surface of the uterus), pedunculated (attached to a stalk), and cervical (located in the cervix) fibroids, are less likely to directly affect fertility unless they alter the shape of the uterus significantly or obstruct the fallopian tubes.