## Estimation Of Crown – Rump Length From External Surface Area Of Frontal And Parietal Foetal Skull Bones

#### Author(s): Kulkarni P.Y. and Zambare B.R.

#### Vol. 55, No. 1 (2006-01 - 2006-07)

Department of Anatomy, Dr. Vaishmpayan Memorial Medical College, Solapur.

### Abstract:

The external surface area of some foetal skull bones (i.e. Frontal & Parietal) were measured in 50 normal foetuses of various age group. These measurements were tabulated and statistically analysed. A linear co relation was observed between the external surface area of parietal and frontal bone and CR length. The regression equation was derived from the available data, with the help of the equation CR length could be estimated and thus the approximate age of the foetus could be determined.

**Keywords:** CR Length , frontal bone, Parietal bone

### Introduction:

Whenever foetal skull bones, viz. parietal and frontal are sent to an anatomist to give an opinion regarding the probable age of the foetus, then it becomes difficult to give an opinion on this matter, due to lack of information in the most of the standard textbooks of Embryology.

Scammon.R.E. (1939), Gary, S.B. et al (1975) and Bartolucci, L. (1975) have reported linear correlationship between occipito-frontal circumference, distance between Glabella and external occipital Protuberance bi-parietal diameter and crown-rump length and foetal age.Similarly Felts, W.J. (1954), Gardner, E and Gray, D.J. (1970), Mehta, L. and Singh, H.M. (1972), and Vare, ccipital po A.M. and Bansal, P.C. (1977) have shown a linear correlation between the diaphyseal lengths of foetal long bones and crownrump length and foetal age.

Kharkar, A.R. and Fakhruddin, S. (1986) have shown a definite linear correlation between the external surface area of foetal parietal bone and crown-rump length. Kharkar A.R. (1993) similarly studied the correlation between external surface area of foetal frontal bone and crown-rump length.

So far no attempt has been made to estimate the foetal age with the help of individual skull bones. Hence the present study is undertaken to establish the correlation between the external surface area of various foetal skull bones and crown-rump length and hence to predict the approximate foetal age from crownrump length.

Occipitofrontal circumference was measured at Glabella and external occipital protuberance.

### Material And Methods:

Fifty apparently normal human foetuses ranging from 120 mm to 410 mm CR length of both the sexes were obtained from the Department of Obstretics and Gynaecology, Chhatrapati Shiivaji Maharaj Sarvopchar Rugnalaya, Solapur. The CR length was measured with the help of an osteometric board.

Each foetus was kept for maceration in running tap water and periodically observed for completion of maceration. At first the brain of foetuses were removed through foramen magnum. Then the skull was kept for maceration. Around two to three weeks were required for complete maceration and separation of the skull bones. Following skull bones from specimen were taken for study, viz. parietal and frontal bone. They were stored in a separate labeled packets for each specimen; before they were taken for measurement.

**Fig. 1:** Showing Parietal bone

**Fig. 2:** Showing Frontal bone

**Fig. 3:** Showing Pariental bone covered with cloth.

**Fig. 4:** Showing cloth spread on graph paper for meansurement of frontal surface.

New cotton cloth was dipped in bucket full of water overnight. Following morning the cloth dipped in water was slightly squeezed to remove the excess of water. This wet cloth was pasted on the external surface of the individual skull bones i. e. parietal and frontal. The outline was marked with the marking pen and care was taken while pasting the cloth on external surface of skull bones to avoid creases on the cloth. Then the cloth was cut according to the shapes of bones. The same wet cloth which was marked was spread on graph paper without creases on the graph paper and its outline was drawn.

### Observations:

CR length was arranged in form of interval of group and mean surface area minimum maximum surface area for frontal and parietal bone were calculated. The values of CR length and surface area of parietal and frontal bone were plotted on the graph. (Graph 1 for Parietal and Graph 2 for Frontal). The observations for individual bones were as follows:

### Parietal Bone:

Surface area of parietal bone min to max range was 3.56-76.74 sq.cm with mean surface area was 37.88 sq.cm.The correlation coefficient for parietal bone was calculated.

The correlation coefficient® for parietal bone was calculated as 0.91. Standard error (S.E.) for® was found by equation and was negligible. Probable error (P.E) was also found to be negligible.

The level of significance was assessed with the help of S.E and P.E which were highly significant. The regression equation of X on Y i.e.

X = Y + 39.18 / 2.9481

With the help of above regression equation for surface areas of parietal bone in the sample, the CR lengths were worked out. The straight line regression equation was then plotted on graph paper (graph no.1.). The regression line was in hand with straight line and was very close to straight line. Also it was found to cut the standard line, at some places. All these characters of regression line indicated that the results were very close to the standard.

Frontal bone: Correlation coefficient calculated was 0.88 and the values of standard error (S.E) and probable error P.E were 0.0319 and 0.0215 respectively shown in table no. 3. While assessing the significance level it was found that the results were significant.

#### Table 1: Showing minimum, maximum and mean surface area for frontal bone and parietal bone.

Group | CR length in cm |
Mean CR length in cm |
Parietal Area Mean Min Max sq. cm |
Parietal Area sq. cm |
Frontal area MinMax sq. cm |
Mean Frontal Area sq. cm |
No. of Cases |
---|---|---|---|---|---|---|---|

1. | 12-17 | 13.63 | 3.56-7.18 | 5.84 | 2.13-6.78 | 5.33 | 4 |

2. | 17.1-22 | 19.75 | 11.76-32.17 | 20.52 | 8.83-18.94 | 13.64 | 11 |

3. | 22.1-27 | 23.73 | 21.38-53.73 | 32.40 | 14.66-27.27 | 19.4 | 11 |

4. | 27.1-32 | 28.88 | 35.53-56.83 | 44.27 | 17.62-29.4 | 22.27 | 10 |

5. | 32.1-37 | 34.11 | 50.05-60.53 | 55.08 | 25.53-34.93 | 30.15 | 10 |

6. | 37.1-42 | 38.66 | 62.58-76.74 | 68.09 | 30.23-34.33 | 32.63 | 4 |

Total | 50 | ||||||

#### Table 2: Showing values of correlation coefficient, S.E., P.E. and level of significance of parietal bone.

1 | Correlation coefficient | 0.91 |

2 | Standard error | 0.02431 |

3 | Probable error | 0.016397 |

4 | Level of Significance | Highly Significant |

5 | Paired ‘t’ test | Highly Significant (p < 0.001) |

#### Table 3: Showing values of correlation coefficient, S.E., P.E. and levels of significance of Frontal Bone

1. | Correlation Coefficient | 0.88 |

2. | Standard error | 0.0319 |

3. | Probable error | 0.0215 |

4. | Level of Significance | Significant |

5. | Paired ‘t’ test | Significant(p < 0.001) |

Regression equation of X on Y

X = Y + 14.7731 / 1.37

With the help of the above regression equation for various surface areas of frontal bone ranging between minimum and maximum areas in the sample, CR length were worked out. The straight line regression equation was plotted against CR length. Regression line drawn was found to lie close the straight line again indicating significant results. (graph no. 2)

### Parietal bone:

In the present study, at mean CR length 14.5 sq.cm., mean parietal area was 5.84 sq.cm. then from 14.5-19.5 range, 1 cm increase in CR increased parietal area by 2.936. sq. cm. From 19.5-24.5, 1 cm increase in CR length increased area by 2.375 sq.cm. Then from 29.5-34.5, 1 cm increase in CR length increased area by 2.162 sq.cm.. From 34.5-39.537 1 cm increase in CR length increased parietal area by 2.602 sq.cm.

### Frontal bone:

At mean CR length 14.5 mean frontal area was 5.83 sq. cm. From 14.5-19.5, 1 cm increase in CR length increased area by 1.152 sq. cm. Then upto 29.5 growth rate was decreased i.e. 0.574 sq. cm. cm. of CR length. Then from 29.5-34.5, 1 cm increase in CR length increased area by 1.576 sq. cm. There after increase in CR length, did not show any significant increase in surface area of frontal bone. i.e. 0.496 sq. cm. cm. CR length.

### Discussion:

In the present study the external surface area of some skull bones of foetus i.e. parietal and frontal were measured to determine their relationship with the crownrump length and thereby to arrive at the age of foetus. Smith, S. (1939) Felts, W.J.(1954) Gray,D.J. and Gardener , E (1969) Gardener, E. and Gray, D.J. (1970) Mehta, L. and Singh, H.M. (1972) Vare, A.M. and Bansal, P.C. (1977) Bagnall, K.M.et al, (1982). Kelemen, E. et al. (1984), in these studies the relationship between CR length and diaphyseal length of long bones were studied.

In the present study relationship between CR length and external surface area of foetal parietal and frontal bones were studied. Growth rate for parietal bone was 2.5 cm and for frontal was 1.07 cm.

Scammon, R.E. (1939), Gary, S.B.,et al (1975) and Bartolucci , (1975) had reported linear correlation between occipito- frontal circumference and bi-parietal diameter with crown-rump length and foetal age.

In our present study, linear correlation between external surface area of skull bones and CR length and from CR length foetal age was determined. In our study instead of circumference and diameter of skull bones, surface area was used as a dimension for calculation of CR length.

Seeds, J.W. and Cefalo, R.C. (1982) and Yagel , S. et al (1986) had combined bi-parietal diameter along with length of long bones. Parker, A.J. et al (1982) studied difference between Asian and European parameters for CR length and bi-parietal diameter.

In the present study instead of measuring diameter of skull, external surface area of skull bones, was used as a dimension for measurement of CR length in Indian (Asian) population only.

Kharkar, A. R. and Fakhruddin, S. (1986) estimated CR length from external surface area of parietal bone. A linear correlation was observed between the external surface area of parietal bone and CR length. Kharkar, A.R. and Fakhruddin, S. (1986) in their study CR length was calculated by following regression equation.

X = Y + 13.87 / 2.13

In present study CR length was calculated following regression equation

X = Y + 39.18 / 2.9481

In the present study CR length was estimated from external surface area of parietal bones. A definite correlation was observed between external surface area of parietal bone and CR length.

Kharkar , A.R. and Fakharuddin, S. (1986) in their study found ‘Chi square test’ statistically significant. In the present study paired ‘t’ test was used to prove the level of significance and was found highly statistically significant.

Kharkar, A.R. and Fakhruddin, S. (1986) in their study observed that at 7.5 cm CR length mean parietal area was 3.8 sq. cm. Thereafter for each 1 cm increase in CR length, the parietal area increased by 3 sq. cm.

In present study at mean 14.5 cm CR length, mean parietal area was 5.84 sq. cm then from 14.5 – 19.5, 1 cm increase in CR length increased parietal area by 2.375 sq. cm. Then from 29.5 – 34.5, 1 cm increase in CR length increased parietal area by 2.162 sq. cm. From 34.5 – 39.587, 1 cm increase in CR length increased parietal area by 2.602 1 sq. cm.

Kharkar, A.R. (1993) studied CR length from external surface area of frontal bone. A linear correlation was observed between the external surface area of frontal bone and CR length.

In their study minimum, maximum and mean surface area of frontal bone were as shown in table No. 3.

Kharkar A.R. (1993) in their study found the regression equation as follows

X = Y + 2.61 / 0.78

Kharkar, A.R. (1993) in their study used “chi” square test for assessing the level of significance and found significant.

At 7.5 cm mean CR length, mean frontal area was 2.95 sq. cm. There was proportionate and steady increase in surface area upto 17.5 cms mean CR length.

For each 1 cm increase in CR length the frontal area increased by 0.6 sq. cm. Beyond 17.5 cm mean CR length, the growth rate was slightly higher i.e. 1.18 sq. cm. cm. of CR length. At 27.5 cm mean CR length growth rate was slow. It is 0.4 sq. cm of CR length.

In the present study CR length was estimated from surface area of frontal bone and definite correlation was observed between surface area and CR length. The regression equation for calculation of CR length was as follows

X = Y + 14.7731 / 1.37

Paired “t” test was used and found to be statistically significant.

At mean CR length 14.5, mean frontal area was 5.83 sq. cm. From 14.5 – 19.5, 1 cm increased in CR length increased surface area by 1.56 sq. cm. From 19.5 – 24.5 ranges, 1 cm increase in CR length increased surface area by 1.152 sq. cm. Then upto 29.5 growth rate decreased i.e. 0.574 sq. cm of CR length. Then from 29.5 – 34.5 ranges, 1 cm increase in CR length increased surface area by 1.576 sq. cm. There after increase in CR length, frontal surface area did not increase significantly. i.e. 0.496 sq. cm cm CR length.

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