The placenta is the most important organ for maintaining and continuing healthy pregnancy. It transfers and exchanges oxygen and contortion needed for the fetus. The estimation of the placenta would demonstrate important information about whatever has happened on the fetus that careful extenuation of the placenta can provide insight regard the inutero-environment of the fetus before delivery. As fetus grows, many changes happen in placenta shape and function that reflect changes in needs of fetus in different growth stages. To achieve these metabolic immunologic and endocrine changes should happen in placental trophoblast.

Placental weight reflects placental development and function and is correlated with maternal age, gestational age, history of maternal diabetes, pre-eclampsia, birth weight, parity route of delivery, infants gender Apgar score and fetal distress. Other factors influencing placental weight includes party, maternal height and weight and serum ferritin contraction (but not serum haemoglobin concentration).
Barker et al reported that growth of the placenta was a predictor of maternal medical diseases including cardiovascular disease, hypertension and diabetes mellitus. Other factors that could affect the placenta weight are race and socio-economic status.
Large placental size and low birth weight have been implicated as factors predicting high blood pressure in adulthood. it has been shown that maternal or fetal diseases(gestational diabetus, severe anemia, hypertension, hydrops fetalis)influence fetal and placental weight. it has been shown that placental weight has a significant role in fetal growth in terms of terms of weight, body length and cord length.

Placenta weight
The delivered placenta is “deflated” compared to its state in utero, a consideration for anyone attempting ultrasound or anatomic correlations. The average diameter of the delivered placenta at term has reported as 18-5cm (range 10-5 to 24.5cm), with a mean thickness of 2.3cm (range 1.1 to 4.1cm). the same source descried the early growth of the placenta as primarily an increase in diameter of the chorionic disc, while in the later stages of gestation, placental weight increased primarily due to increase in placental thickness. They likewise reported that mean diameters of the placenta at the third to six months as 5.8cm 8.2cm, 10.8cm, and 13.0cm, respectively the number of major villous trunks remains constant; therefore, placental growth requires that each major trunk (established in the early months of gestation) must arborize or otherwise develop proportional to the increase in placental weight from early gestation to delivery. Schneider has recently reviewed the ultrasound data regarding placental volume in the mid trimester. The mean increase in placental volume between 16 and 24 weeks was 31, - +, 8cm3; further placental volume in the second trimester was dusty correlated with infant birm weight, suggesting that mid trimester placental well being is an important determine of late fetal grown.
Expected Fetal and Placental Weight Ratio
Weight (g)
Weight (g)
1 -1
0 -18

Most of the eight gained during pregnancy is attributed to the uterus and its contents, the breast increase in blood volume and extra cellular fluid. A smaller fraction of the increased weight as the result of metabolic alterations known as maternal reserves (Cunningham et al 2005).Approximately 62% of the weight gained consists of water, which is retained in all system of the body.
While initial maternal weight and the weight gained during pregnancy are highly associated with birth weight, it remains unclear what role maternal fat or water have in fetal growth. studies in well nourished women at term suggest that maternal body water rather than fat contributes more significantly to infant birth weight(Cunningham et al 2005).The recommended patten for normal weight gain is approximately 3kg in the first trimester followed by about 0.4kg/week for the remainder of the pregnancy. This pattern results in approximately 3kg of fat stores accumulating in the first half of pregnancy. While weight gained in the second half goes towards the growth of the fetus and maternal supportive tissues.
Fetal growth is slow in the first 2months during organogenesis but then accelerates rapidly. maximum growth rate is achieved between the 4th and 8th month when the fetus grows at the rate of 5-9% per week .Until 15-16weeks the placenta is larger than the fetus but by term the fetus is five to six times heavier than the placenta. Amniotic fluid increases from 7ml at 8weeks, 30ml by 10weeks, 190ml by 16weeks, to a mean of about 800ml by 35weeks after which it decreases to about 400ml by 42weeks.The increase in the weight of the uterus is more rapid in the first 20weeks (Blackburn 2007),the weight of the breast, blood volume and total body water increases steadily thought out pregnancy. The pitting oedema of ankles and legs, which is seen in most pregnant women, especially at the end of the day may amount to over 1L.
There is currently no official recommendation for weight gain during pregnancy. Weight gain averages between 11 and 16kg but variations are large. A birth weight of 3.1-3.6kg has been associated with optimal maternal and fetal outcomes. Maternal nutritional status at the time of conception is very important for fetal growth and development, it is important to attain a healthy body weight prior to conception.

Table showing the distribution of an average increase in weight         
Maternal                Weight gain (kg)           Percentage of total Wt
Uterus                                                0.9
Breast                                     0.4
Fat                                                       4.0                                           64%
Blood                                     1.2                              
Extra cellular fluid               1.2
Total                                                   7.7                                          
Fetus                                       3.3                                           25%
placenta                                             0.7                                           11%
Amniotic fluid                                  0.8
Total                                                   4.8                              
Grand total                            12.5                                                                                       

The placenta weight and fetal weight
 The ability of the fetus to grow and thrive in utero depends on the placental function and the average weight of the placenta at term is 508g. The ratio between placenta weight and birth weight of the newborn is 1: 6. However, methods of measurement vary widely particularly due to differences in placental preparations. 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 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.
Clinical associations with placental weights and fetal placental ratio have been documented; for example, small placentas maybe associated with trisomies where as large placentas may be associated with maternal diabetes. Disproportionately large placentas (low fetal/ placenta ratio) could reflect acute placental injury resulting in villous edema or a chronic process requiring placental overgrowth, such as maternal anemia or malnutrition. Disproportionately small placentas (high fetal/placenta ratio) maybe seen in maternal hypertension, and may result in fetal distress or low Apgar scores. Recent birth weight tables shows fetal birth weights at term have increased overtime. There is a positive correlation between fetal weight and placental weight.
            One of the influencing factors on placental weight is gestational age. Gestational age is known as a principle and determinant fact of placental weight. Kinare et al stated that the capacity of fetal weight growth is determined by placental growth and between placental volume in 15 to 18 weeks gestation ages to placental weight at birth and birth weight found significantly correlation. Placental weight increases in infants proportionately with gestational age, while in infant with small for gestational age (SGA) were not seen any change from 36 weeks gestation. Lo et al have proved there is no significant difference between placental weight and gestational age. In different studies it has been demonstrated that male fetuses gain significantly greater weight as compared to female fetuses from the 34th -42nd week of gestation. Because placental weight has a relationship with infant weight these should be a significant correlation between infant sex and placental weight.

Baby’s Weight
 In first world nation the average weight of a full-term newborn is approximately 3.4kg (7½ lbs), and is typically in the range of 2.7-4.6kg (5.5-10 pounds) over the first 5-7 days following birth the body weight of a term neonate decreases by 3% - 7% and is largely as a result of the reasorbtion and urination of the fluid that initially fills the lungs, in addition to a delay of often a few days before breast-feeding becomes effective. After the first week healthy term neonates should gain 10-20 gram/kg/day.

Factors that determine the Birth weight of a baby
·                    Infant gender
·                    Multiple factors
·                    Size of the parents
·                    Birth order
·                    Baby’s health
·                    Maternal factors such as race and ethnicity, nutrition and current and previous pregnancy medical risk characteristics.

There is an increase weight gain during pregnancy especially the first half of pregnancy. While weight gained in the second half goes forwards the growth of the fetus. Fetal growth is slow in the first two months during organogenesis but this accelerates rapidly maximum growth rate is achieved between the 4th and 8th month when the fetus grow at the rate of 5-9% per week. Until 15-16 weeks the placenta is large than the fetus but by term the fetus is five to six times heavier than the placenta.
            It was reported that an altered growth of placentas was a predictor of maternal medical diseases including cardiovascular disease, hypertension and diabetes mellitus. Other factors such as race and socio-economic status also affect the placenta weight. Also a woman with diabetes mellitus tends to have a large baby than a normal pregnant woman.
            Studies have shown that the male fetus gain significantly greater weight when compared to female fetus from 34th to 42nd week of gestation. Because placental weight has a relationship with infant weight, there should be a significant correlation between infant sex and placental weight.                     

Barker DJ, Bull AR, Osmond C, Simmonds SJ. Fetal and placental size and risk of hypertension in adult life. BMJ. 1990 Aug 4;301 (6746): 259-262.
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Cunningham F, Leveno K, Bloom et al 2005 Williams obstetrics, 22nd education, mcGraw-Hill, New York.
Cunningham FC, Gant NF, Leveno KJ, Gilstrap LC, Hauth JC, Wenstrom KD. Williams Obstertic. 21st ed. Philadelphia: McGraw Hill, 2001. P. 558-559.
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Hindmarsh PC, Geary MP, Rodeck CH, Jackson MR. Kingdom JC. Effect of early maternal iron stores on placental weight and structure. Lancet. 2000 Aug 26;356 (9231): 719-723. 
Kinare AS, Natekar AS, Chinchwadkar MC, Yajnik CS, Coyaji KJ, Fall CH, Howe DT. Low midpregnancy placental volume in rural Indian women: A cause for low birth weight? Am J Obstet Gynecol. 2000 Feb; 182 (2): 443-448.          
Lo YF, Jeng MJ, Lee YS, Soong WJ, Hwang B. Placental weight and birth characteristics of healthy singleton newborns. Acta paediatr Taiwan. 2002 Jan-Feb; 43 (1): 21-25
Thame M, Osmond C, Wilks RJ, Bennett FI, McFarlane-Anderson N, Forrester TE. Blood pressure is related to placental volume and birth weight. Hypertension. 2000 Feb; 35 (2): 662-667.
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