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January 1982, Volume 32, Issue 1

Original Article

Maternal Blood Groups and Differential Fertility: A Hospital Survey from Lahore

S.A. Shami  ( Department of Zoology, Government College, Lahore, Pakistan. )


The present study is based on a sample of 587 mothers and 1656 pregnancies. The results show that O-positive and B-positive mothers are more successful in reproduction and indicate low percentage of prenatal loss (stillbirths+abortions) than mothers from other ABO groups. Favourable age of marri­age for O-positive and B-positive mothers is suggested between 15-22 years and 23-30 years respectively. Rh-negative mothers show significantly low livebirths, but higher prenatal loss than Rh-positive mothers.
Rh-negative mothers (AB- + B- than A- ± 0-) have significantly higher male births than in Rh-positive mothers. (AB + B+ than A++0+). (JPMA 32:2, 1982).


ABO blood groups in man have been studied for their frequency distribution, association with ci iseases and maternal-foetal incompatibility. Brues (1954) was of the opimon that the ABO blood group polymorphism is maintained by natural selection, fir which she constructed a svstem of selection coefficients favouring compatible A0, BO and AB zygotes. Chung and Morton (1961) suggested that her method cannot distinguish between differentia’ ferti1 ity and mortality. They found that maternal-foctal mcormpatibillty significantly reduces fertility and causes elimination (.f incompatible zygotes.
It is ditfficult to collect family data for the examination of reproductive ditlerences in reciprocal matings. Effi)rts have been made to detect differences in fertility associated with the ABO blood groups from the records of the Blood Transfusions Service (Bennett and Walker, 1955). The present study on differential fertility and materna1 blood group is based on a sample women admitted to local hospitals.


Material and Subjects

Data were collected from Sir Ganga Ram Hospital and Lady Willingdon Hospital, Lahore. Married women admitted in the hospitals at the time of survey were typed for A-B-0 and Rh-(positive and negative) blood groups. They were interviewed to obtain information regarding age at the time of the first birth and in the successive births; number of children born, their sexes and birth order; number of stillbirths, abortions anti Postnatal deaths.
The number of mothers scored was 587. The number of pregnancies recorded was 1656, of which 1247 were livebirths (648 males; 599 females), 159 stillbirths and 250 abortions.


Maternal ages were grouped into 5 classes (<15-18, 19-22, 23-26, 27-30 and 31-34+ years).

Table I gives the distribution of maternal blood groups in different age groups. The highest percentage of mothers is associated to B+ (32.71) and O+ (25.04) blood groups. The lowest representation is that of AD- (1 .70%) mothers. The sample shows the highest number of Rh+- mothers (85.52%).
Livebirths, deaths, stillbirths, abortions and total number of pregnancies in each maternal age group for different ABO blood groups are shown in Table II.

TPrecentages of livebirths, stillbirths and abortions were calculated by dividing with the total number of pregnancies in each class, and percentage deaths from the total number oflivebirths. The highest livebirths are seen in O+ (79.80%) and B (78.50%) mothers respectively. The lowest percentage of births (64.21) is in B- mothers. Mothers with O-, A-, B- and AB- blood groups indicate comparatively less number of livebirths than their positive counterparts. The highest percentage of postnatal deaths of offspring are seen in AB- mothers (36.86%) and the lowest in B- mothers (6.56%). The stillbirth rates are higher in B- mothers (20.00%) and the lowest in 0- mothers (4.08%). Abortions are the highest in 0- mothers and the minimum in O+ mothers (12.12%). Total prenatal loss (stillbirths+abortions) observed is the highest in B- mothers (35.79%) and 0 mothers (34.69%) while the lowest prenatal loss is seen in O+ mothers (20.20%) and B+ mothers (21 .86%). The highest percentage pregnancies are observed in B+ mothers (33. 19) and the lowest in 0 mothers (2.96).

Table III shows the distribution oflivebirths, deaths, stillbirths, abortions and pregnancies in different age groups of Rh-positive and Rh-negative mothers. Rh-positive mothers show highest I ivehirths (76.70%) than Rh-negative mothers (66. 13%). A higher percentage of stillbirths (12.09) and abortions (21.77) are observed in Rh-negative mothers. The differences in the number of stillbirths and abortions in Rh-positive and Rh-negative mothet s arc statistically highly significant (X22=l3.75; P~0.0O1). Total prenatal loSs in Rh-positive mothers (23 .08%) is less than in Rh-negative mothers (33.87%). The highest prenatal loss in Rh-positive mothers in seen between ages 23-26 years (27.89%) and 19-22 years (24.72%) while in Rh-negative mothers in the age groups 27-30 years (51 .72%) and 23-26 years (33.33%). Mothers between 3 1-34+ years of age have the lowest prenatal loss in Rh-positive (13 .64%) and Rh-negative mothers (28.75%). However, postnatal deaths are the highest in this age group in Rh-positive (25.31%) and Rh-negative mothers (30.00%).
The livebiith data were arranged in relation to family size and ABO maternal blood groups (Table IV).

TThere is no appreciable difference in the family size of mothers belonging to different blood groups. The mean flirnily size and variance of the total sample is 2. 12 and 3 .98 respectively. The data contain a small number (26) of childless mothers of which the highest number is that of B+ mothers (42.30%).
Table V shows the distribution of sons and daughters born to mothers ot diflerent ABO groups. The highest male births is observed in AB-negative mothers (0.7895) and thc lowest is seen in O-negative mothers (0.4375). Rh- positive mothers show higher male births (0.5254) than Rh-regative mothers (0.4817).


The present study indicates the presence of a higher percentage cf B+\\ (32.71) and O+ (Z5 .04) mothers. These two types of mothers show the highest percentage of livcbirths (0+ =79.80; B~=78 .50). Stillbirths, abortions and Iivebirths in O+ and 11+ mothers are significantly different from those in A+ and AB+ mothers (X22=6.28; P<0.05). In O++B+ mothers the observed number of stillbirths and abortions is less than the expected iiumber and a higher number of observed Jivebirihs than the expected one. Mcthers with A+ and AB+ blood groups possess higher number of observed stillbirths and abortions and lesser number of I ivebirths than the expected value. In a similar comparison, when O- and B- mothers are compared with A+B mothers for stillbirths, abortions and livebirths he results are statistically non-significant (X2=2 .02; P> 0.30). The differences in the number of stillbirths, abortions and livebirths in Rh-positive and Rh-negative mothers are statistically highly significant X 2= 13.75; P <0.001).
O-positive mothers at younger age <15-18 years (81 .34) and 19-22. years (81 .53) show the highest percentage of livebirths and the lowest prenatal loss 18 .65% and 18.47% re-specively. The condition is somewhat different with B-positive mothers which show comparariveIy less livebirths (80.24% and 72.91%) in the two younger age groups, but higher percentage of prenatal loss (19.76% and 27.09%). In the next two higher age groups, 23-26 year and 27-30 years, B-positive mothers show higher percentage of livebirths (79.63 and 92 68) and low prenatal loss (20.37% and 12.19%) compared with 0+ mothers (Iivebirtns, 74.28% and 73.33%; prenatal loss 25.71% and 26.62% respectively). These results indicate that 0+ mothers marrying at younger age bear more live-births and low prenatal loss, but for B+ mothers the years between 23 and ‘30 seem favourable age for marriage.
B-positive and O-positive mothers show comparatively higher percentage of pregnancies (33 .27%) and 23.91% respectively) than otner ABO-mothers.
The results suggest that selective forces operate against the offspring of Rh-negative mothers and significantly favour those from the Rh-positive group, particularly O-positive and B-positive. There is some indication, too, for age specific action of selection but this cannot be generalized due to lack of large body of data. Bennett and Walker (1955) gave no indication of differences in fertility associated with ABO blood groups but they did observe reproductive differences between individuals. Matsunaga and Itoh (1958), Chung and Morton (1961), who typed both the parents for ABO blood groups, showed that maternal-foetal incompatibility reduces fertility. The present data lack such information.
AB-negative mothers show the highest number of male births. Plank and Buncher (1975) showed highest male births in AB mothers (both Rh+ and Rh-). Allan (1972) observed significantly higher male births in Rh-negative sibs (AB- + B- and A- + O-) than Rh-positive (AB+ ± B+ than A+ + O+). The present findings also indicate that Rh-negative (AB- 4- B- than A- 4- 0-) mothers have significantly higher male births 21=4 .08; P <0.05) but non-significant (X 21=0 .07; P> 0.70) male births in Rh-positive mothers (AB+±B+ than A+±O+).


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