The human placenta develops with the principal function of providing nutrients and oxygen to the foetus  - . Adequate foetal growth and subsequent normal birth weight depend on the efficient delivery of nutrients from the mother to the foetus via normally functioning utero-placental organ  - . It is clear that normal development of placenta during gestation is necessary for support of a healthy foetus  . The average weight of placenta at birth is 508 g . However, methods of measurement vary widely particularly due to differences in placental preparations before weighing .
Placental weight and its relationship to infant size at birth have been studied for more than a century. Past studies indicated that placental weight was associated with pregnancy outcome. High placenta weight was associated with a poor perinatal outcome, a low Apgar score, respiratory distress syndrome and perinatal death; whereas a low placental weight was associated with medical complications in the mother  . It has also been reported that altered growth of the placenta was a predictor of maternal medical diseases including cardiovascular disease, hypertension and diabetes mellitus   . Other factors such as race and socioeconomic status also affect the placental weight  - .
Careful examination of the placenta can provide insight regarding the in-utero environment of the foetus before delivery. There is a positive correlation between foetal weight and placental weights . The standard method of weighing the placenta, after trimming the placental disk off membranes and umbilical cord, may also merit simplification. Leary et al. suggested that the foetal weight/placental weight correlation does not change when placentas are weighed trimmed compared to when they are weighed untrimmed  - . The placenta can be weighed with membranes and cord attached, but the standard approach since its proposal by Benirschke in the early 1960s is to weigh the placenta after the extra placental membranes and the umbilical cord are trimmed from the disk . This limits the measurement to the weight of the placental disk, the actual nutrient exchanging part of the placenta. However, Leary et al. suggested that trimmed and untrimmed placental weights are exchangeable, based on their high correlation  . Paucity of report in literature on placental weight and its relationship to the weight of the neonate at birth in Abakaliki informed this study. Therefore the aim of this study was to determine the relationship between placenta weight and birth-weight of neonate in our hospital.
2. Materials and Method
Study area: Alex Ekwueme Federal University Teaching Hospital (formerly known as Federal Teaching Hospital) Abakaliki is a tertiary hospital within Abakaliki metropolis. The hospital is made up of ten clinical departments; Obstetrics and Gynaecology, Paediatrics, Medicine, Surgery, Psychiatry, Community Health, Family Medicine, Ophthalmology, ENT and Anaesthesiology. Department of Obstetrics and Gynaecology is one of the ten clinical departments in the hospital, it has ten teams with each comprising consultants, senior registrars, registrars, senior house officers and house officers. The department runs gynecological clinics, preconception, antenatal, intrapartum, and postnatal services. It is also a referral centre to the surrounding maternities and hospitals and also receives referral from surrounding states: Cross Rivers, Enugu, and Benue states.
Study design: This was a retrospective study conducted at Alex Ekwueme Federal University Teaching Hospital, Abakaliki. The study cohorts were women delivered at term (37 to 42 weeks) between 1st January 2013 and 31st December 2015. A pre-designed proforma were used to extract patients’ information on gestational age at delivery (in weeks), parity, mode of delivery, foetal birth weight, placental weight, foetal gender, and presence or absence of maternal medical diseases. The inclusion criteria included that the pregnancy must be term and singleton. Exclusion criteria included retained placenta, multiple pregnancies and morbidly adherent placentae.
Data analysis: Data analysis was done using Epi Info software (7.2.1 CDC Atlanta Georgia) and statistical analysis performed using one way analysis of variance. The results were expressed as frequency tables, percentages, pie charts, mean and standard deviation. The relationships between categorical data were analyzed using χ2, with a P-value of 0.05 considered statistically significant and correlation coefficients were calculated using Pearson’s formula. Odd ratios were also calculated.
Ethical consideration: Ethical approval for the study was sought and obtained from the Research and Ethical Committee of the Alex Ekwueme Federal University Teaching Hospital, Abakaliki and the study duration approved for the study was 1 year.
Out of a total of 2417 total deliveries within the study period, 2215 mothers met the inclusion criteria constituting 91.6% of deliveries during the period. The remaining 202 (8.4%) women were excluded from the study due to incomplete documentation in their hospital notes. Two thousand one hundred and six hospital folders were retrieved constituting 95.07% folder retrieval rate. The placental birth weight ratios (PBWR) were calculated by dividing placenta weight by birth weight of the neonate and multiplied by 100.
Table 1 shows the maternal characteristics, perinatal outcome and placental birth weight ratio. The ages of the patients ranged from 16 to 42 years with a mean of 29.11 ± 5.3 years. The relationship between increasing maternal age and placenta weight ratio was not statistically significant (P = 0.283). The mean parity
Table 1. Relationship between maternal age and booking status with placenta birth weight ratios.
NS = not statistically significant.
of the subject was 1.79 ± 3 with a range of 0 - 9). One thousand, six hundred and ninety eight patients (80.63%) were booked while 408 (19.37%) were unbooked. The relationship between booking status of the patient and placenta weight ratio is not statistically significant (P > 0.05).
The average gestational age at delivery was 39.5 ± 3.8 weeks with a range of 37 - 42 weeks as shown in Table 2. The relationship between increasing gestational age and placenta birth weight ratio was statistically significant (P < 0.0001).
One thousand, eight hundred and eighteen patients (86.30%) had spontaneous vertex delivery while 288 (13.70%) of the patients had caesarean section (Table 3). The relationship between mode of delivery and placenta weight ratio is not statistically significant (P > 0.05). The mean birth weight and placenta weight from caesarean section were comparable to those from vaginal delivery (3444 g vs 3320 g) and (628.7 g vs 603.98 g), respectively and was not statistically significant at (P > 0.05). One hundred and one fetuses, constituting 4.8% of fetuses suffered perinatal mortality.
The mean neonatal birth weight was 3344 ± 488 g with a range of 2200 - 5100 g while the average placental weight was 617 ± 72 g with a range of 400 - 1300 g. The mean PBWR was 19.94 ± 4.2 with a range of 14.28 - 38.22 as depicted in Table 4. The PBWR decreases from 37 weeks to 39 weeks gestation after which it started increasing up to 42 weeks gestation.
Both the placental and neonatal birth weights increase with advancing gestation (with the latter increasing more than the former). This relationship is depicted in Figure 1 and Figure 2. The correlation coefficient (r) between the placental weight and foetal birth weight was 0.968 (reflecting a strong positive correlation).
Table 2. Gestational age and placenta birth weight ratio.
Table 3. Mode of delivery and perinatal outcome with placenta birth weight ratio.
SVD: spontaneous vertex delivery; CS: caesarean section; NS: not statistically significant.
Table 4. Mean neonatal birth weight (g), placental weight (g), and placental-birth weight ratio by gestational age at birth.
GA: gestational age; SD: standard deviation; BW: birth weight; PW: placenta weight; PBWR: placenta birth weight ratio.
Table 5 shows the distribution of mean birth weight and placental weight by parity. Majority of the patient seen (92.12%) have low parity between 0 - 4, while 7.88% of the patients seen were grand multiparous women. There is a slight increase in mean placental weight with increasing parity up-to to the fifth parity, but there was a decrease at parity of six and above. However, increasing parity did not have any significant effect on placenta birth-weight ratio (P value = 0.0329).
Figure 1. Correlation between the mean birth weight and gestational age.
Figure 2. Correlation between mean placenta weight and gestational age.
Table 5. Mean birthweight and placental weight by parity.
BW means birth weight; PW means placenta weight; PBWR means placenta birth weight ratio; P value = 0.0329 indicating a positive but weak correlation.
The sex ratio (male to female) was 1.1:1. The distribution of birth weight by gender is shown in Table 6. The mean birth weight of male babies (3389 g) was higher than that of their female counterpart (3304 g) and the placenta birthweight ratio for male was higher than female. However, these were not statistically significant (P > 0.05).
Table 7 depicts the distribution of mean placental birth weight ratio in relation to maternal medical conditions. The study showed that maternal medical conditions have no effect on mean placental birth weight ratio (P = 0.063).
Table 8 showed the relationship between Placenta and Birth weight ratio and the immediate fetal outcome. One thousand, nine hundred and five (90.5%) patients had PBWR that ranged between 15 and 24. Twenty five percent (25%) of babies delivered with PBWR of less than 15 were admitted into NICU for moderate to severe birth asphyxia and 40% of them suffered perinatal death. Also, 30.9% of babies with PBWR that ranged between 25 and 29 were admitted into NICU and 11.1% of them suffered perinatal death. For babies with PBWR of 30 - 34, 54.45% of them were admitted into NICU whereas remaining 45.45% suffered perinatal mortality. All the babies with PBWR of greater than 35 suffered early perinatal mortality. The correlation coefficient (r) between the PBWR and immediate neonatal outcome was 0.7104 (reflecting a positive correlation).
Table 6. Mean birth weight (g) and placental weight (g) by foetal gender.
SD = standard deviation; BW = birth weight; PW = placenta weight; PBWR = placenta birth weight ratio; P value = 0.598.
Table 7. Placental weight (g) in relation to maternal medical conditions.
Table 8. Placenta birth weight ratio (PBWR) in relation to immediate fetal outcome.
PBWR = placenta birth weight ratio; NICU = neonatal intensive care unit. The correlation coefficient (r) between the PBWR and immediate neonatal outcome was 0.7104 (reflecting a positive correlation).
Placental weight and birth weight of the neonate are widely available measures. The ratio of these two variables is a useful marker of foetal nutrition and utero-placental function. The mean placental weight of 617 g in this study is comparable to 623 g reported in North-central Nigeria but lower than 643 g reported in Western Europe  . However, it is more than 588 and 590 g reported in Northern Nigeria and Ukraine respectively  . The variations in the mean weight of the placenta may be due to variations in the methodology of preparing and weighing the placenta together with cord clamping time  . It has also been reported that ethnicity may affect the placental weight . The mean birth weight of the neonate in this study (3344 g) is lower than 3425 g and 3382 g reported in Ukraine and Western Europe, respectively; but higher than 3065 g and 3275 g reported in two different studies in Northern Nigeria    . These differences in mean birth weight may be due to altitude, race, genetics, maternal nutrition and maternal diseases .
The mean PBWR of 19.94% in this study is similar to 20.0% and 20.24% reported in Western Europe and North-central Nigeria but higher than 13.9% and 18.2% reported in Ukraine and Northern Nigeria, respectively    . The positive correlation between the placental weight and neonatal birth weight noted in this study has been observed by previous authors   . The decline in PBWR with increasing gestational age at term observed in the present study has been reported by previous authors   . An abnormally high PBWR (i.e. low neonatal weight relative to the placental weight) is thought to indicate an abnormal placenta with impaired function as in human immune deficiency virus infection, obesity, maternal anaemia, cigarette smoking and low socioeconomic status   . As shown in this study, Infants with such abnormal ratios are at increased risk of NICU admission and perinatal death, and this correlates with previous studies  .
A placenta weight to birth weight Ratio (PBWR) range of 15.0% to 24.9% is optimal for foetal survival according to this study. Conversely, an abnormally low PBWR (<15.0%) indicates foetuses with presumed reduced placental reserves and carries poor perinatal outcome. Such foetuses tend to show asymmetric growth restriction, suggesting that the small placenta limits optimal foetal growth with poor immediate neonatal outcome and this was in accordance with previous studies  . From this study, PBWR of lower than 15% and higher than 24% are associated with poor neonatal outcome. This observation is slightly different from what was earlier reported by Chandrakant et al. . Chandrakant et al. reported that a PBWR of ≤15.99% was low, 16% - 19.9% was normal and ≥20% was high and that PBWR of ≤15.99% and ≥20% are associated with poor neonatal outcome. This observed difference may be due to differences in placenta preparation. However, both studies agreed that abnormally low and high PBWR are associated with poor perinatal outcome.
The socio-demographical data of patients in this study is comparable to what was reported in the previous studies. The age range of the subjects in this study 16 - 42 years is similar to the age range of 16 - 38 years reported in a previous study done in Sokoto . Just like in the earlier studies, the relationship between maternal age and PBWR is not statistically significant. The mean gestational age in the study (39.5 weeks) is also similar to 39.7 weeks and 39.9 weeks reported in western Europe and North-central Nigeria, respectively, but higher than 38.8 weeks reported in Sokoto   . According to this study, the relationship between advancing gestation and PBWR is statistically significant and this is similar to what was reported in the previous studies    . Most of the women enrolled for the study were booked patients (80.63%) because most of the unbooked patients did not satisfy the inclusion criteria for the study. As shown in this study, booking status has no statistically significant effect on PBWR. The mean birth weight of babies delivered by caesarean section in this study was lower than those delivered vaginally while the placental weight was higher in the former than later. Similar observation had been made in previous studies  . Differences in cord clamping time have been suggested to explain these differences, since the umbilical cords are frequently clamped relatively late in vaginal delivery (so as to optimize blood transfer to the fetus) while in caesarean section early clamping of the cord is usually the rule . Furthermore, due to the absence of uterine contractions during caesarean section, the intervillous space in the placenta is more expansive and likely to contain more maternal blood than in vaginal deliveries where maternal blood is squeezed out of the placenta by contraction of the uterus  . However, mode of delivery has no significant effect on PBWR.
Relative increase in both placental and neonatal birth weight associated with increasing parity up to Para 5, then gradual decline in the placenta and neonatal weight from 6th parity upward was similar to what was earlier obtained in central Nigeria  but was not in agreement with Azupurua’s report that the weight of placentae and babies from multiparous women are higher than those primigravid and primiparous women .
The limitations of this study include poor record keeping in most of our centres, which makes obtaining information of patient cumbersome. Also, most of the data obtained from this study were gotten from labour record and patients’ folders with a lot of individual differences in measurement and recording of patients’ information by various cadres of health workers involved. A prospective study that will use limited number of patients with the same researcher and measuring scale is suggested.
In conclusion, this study has shown that there is a positive correlation between the placental and infant weight. In addition, the ratio of the placenta and foetal weights at term increases with advancing gestational age. Also, sociodemographic data of the mother and maternal medical condition have no statistically significant effect on placenta birth weight ratio. A PBWR of between 15 and 24 is optimal for good immediate neonatal outcome. A PBWR of higher than 24 or lower than 15 is associated with poor perinatal outcome. Therefore, factors causing abnormally high or low PBWR will result in poor immediate perinatal outcome. Recognizing such abnormal value of PBWR will help to expedite actions that will help to prevent poor immediate perinatal outcome.
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