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In the majority of pregnancies, the length, weight and head circumference of the baby is generally a good match for the size and shape of the mother's pelvis, allowing for a safe passage for birth. A woman who genetically has a small stature is likely to give birth to a petite baby, and a woman with a larger build is likely to have a bigger baby. If a baby who is 10 pounds, tries to squeeze through the pelvis of a mother which is designed for a 6 pound baby, it would be an example of pelvic disproportion.
An obstetrician can make an educated guess about the size of a woman's pelvis utilizing estimates taken early in the first trimester of pregnancy. If there is any concern that the pelvis is not in proportion to the baby's size, a diagnostic ultrasound can be used to confirm the measurements.
 Minor disproportion
If the disproportion is only minor, a woman's obstetrician may allow her to try a vaginal delivery, on the condition that there are no other complications. The baby may still be able to born in this way, due to the unique properties of its head, which is able to be molded pressures of the birth canal. A woman’s pelvis may also expand enough to allow the baby through.
 Major disproportion
If there is quite a large difference in size ratios, the obstetrician will arrange a cesarean delivery.
 If this problem is undetected
If this condition is not detected during pregnancy, and a major disproportion exists, a woman may have an extremely troublesome labour. The baby's head will not be able to fit through the pelvis, inevitably resulting in an emergency cesarean delivery.
 When not to worry
A woman does not need to be concerned about this condition if the baby's head has become engaged during the latter weeks of pregnancy, as it strongly suggests that the baby's head can be delivered through the pelvis with the minimum of difficulty.