REPORTS have shown an increasing incidence of multiple births. In Canada a number of multiple births have increase to 35 percent, and in the United States the number of multiple deliveries had increase to 65 percent.

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There are several factors that contribute to the increasing incidence of multiple births:

Infertility treatments:

Infertility treatments with ovarian stimulants and in-vitro fertilization, are more than ten times to result in twin pregnancies and that 13 to 26% of pregnancies from infertility treatments were noted to be multiple as compared to only 1.0% to those who conceived naturally.

Racial variations:

The frequency of twin pregnancies is lowest among Asians and highest in Africans and East Indians. Non-white Americans have about 13.5 twin births per 1000 pregnancies as compared to less than 10 twin births in white Americans. The difference in frequencies of twin pregnancies was mostly due to the higher rates of fraternal multiple births.

Number of previous births and maternal age:

Previous number of births and maternal age contribute to the increase in frequency of multiple births. Noted are the increase incidences of twin births after the second pregnancy and the tendency of multiple pregnancies in women who are older. Women in their early 20’s have about 22 deliveries of twins for every 1000 pregnancies as compared to 50 twins’ deliveries for women over 40.

Familial and environmental factors:

There is a higher incidence of multiple births in some families with history of fraternal twins. Some data have suggested that the increase occurs only in female relatives who have twins. Aunts of fraternal twins on the mother side have about 27 times more likely to have twins and that the fraternal twins themselves are 3 times more likely to have twin pregnancies. Data on interracial marriages have shown that the paternal side of fraternal twins has nothing to do with the increase frequency of multiple births.

The rate of multiple births is also affected by environmental stress and deprivations. For example, during armed conflicts the rate of twin pregnancies and deliveries were noted to increase and to return to normal rates few years after the resolution of the conflict. 

Problems: 

All multiple pregnancies are considered high risks. Complications are much higher. Women who are carrying multiple babies should be followed up more closely for they are at increased risks of developing the following problems: 

Pre-eclampsia

  

Pre-eclampsia is a maternal condition during pregnancy marked by the presence of high blood pressure, swelling of the ankles and presence of protein in the urine.

Pre-eclampsia sometimes may progress into a severe condition known as eclampsia characterized by persistent very high blood pressures and convulsions.

Pre-eclampsia occur in 8 to 10 percent of twin pregnancies as compared to less than 4% in singles. The condition tends to increase to 19% in triplets and much higher in the higher order multiples especially those brought about by fertility treatments.

Twin-to-twin transfusion syndrome

In monozygotic multiple pregnancies, the membrane covering that surrounds or envelope the embryos can either be shared or separate. Sharing of the embryonic membrane or covering are often accompanied with: Vascular problems such as twin-to-twin transfusion.

In twin pregnancy twin-to twin transform occur when one twin (donor fetus) transfuse his blood to the other twin (recipient fetus). The donor twin will become anemic (deficient) and the recipient twin will become plethoric (excess).

Twin-to twin transfusion is due to abnormal blood vessel connections from shared embryonic membrane. Blood from the donor fetus is drained to the recipient fetus through these abnormal vascular connections. This problem often occurs in about 10-15 percent of twin pregnancies. The recipient fetus who is receiving more blood will overburden its heart to pump out the excess blood beyond its capacity leading to heart failure.

The donor fetus that is losing blood will become anemic. The heart will also be stressed to pump out more blood to overcome the deficit eventually the heart will also fail. In some cases where the draining of the blood from one fetus to the other happens very slowly, the donor fetus will be smaller than the recipient fetus who will be larger. The smaller fetus not only will weigh less but is also shorter and has a smaller head circumference.

Growth problems

          

Growth problems may arise when the fetus does not grow appropriately with the increasing duration of pregnancy. Factors like pre-eclampsia, twin-to-twin transfusion, maternal nutrition, infection and the overcrowding of the uterus (womb) beyond its capacity to accommodate the multiple numbers of babies are the common causes of fetal growth problems.

The fetal growth patterns of twins, triplets or more differ from the growth of a single fetus. At the beginning of pregnancy the fetus whether single or multiple grow evenly until the later part of pregnancy when the multiple fetal growths decrease so that at the end of pregnancy multiples usually weigh less than singles.

In twin pregnancy, female twin babies have a longer duration of pregnancy with lower birth weights than male twin babies. However, twin pregnancies of unlike sex the male babies are noted to have higher birth weights than their female twin.

Congenital anomalies

Congenital malformations were observed to be higher in multiples than in single pregnancies. The anomalies are mostly cardiovascular and musculoskeletal.

Congenital malformations were common in multiple pregnancies as a result of infertility treatments than those conceived naturally. Some of the congenital malformations were from uterine compression deformities as a result of overcrowding of many babies more than the uterus can accommodate. (To be continued)