Prediction of Parturition in Dogs and Cats: Accuracy at Different Gestational Ages
Author's address (for correspondence): Michela Beccaglia, Ambulatorio Veterinario Beccaglia, Via PR Giuliani Ang Via Volta 2, 20851 Lissone (MB), Italy. E-mail: firstname.lastname@example.org
In bitches and queens, the ultrasonographic measurement of extrafoetal and foetal structures allows the evaluation of gestational age and the prediction of the parturition term for an extended period of time. The aim of this study was to investigate whether the accuracy of parturition date prediction is affected by the week of pregnancy when the ultrasonographic examination is performed. The results were obtained by retrospective analysis on the gestational period basis (from week 4 to week 9 of pregnancy) in 495 ultrasonographic examinations of pregnant bitches (small and medium size) and 60 of pregnant queens. They demonstrated that a similar accuracy (p > 0.05) was obtained by the measurement of inner chorionic cavity at week 4 and 5 of pregnancy (±1 day, 81% vs 67.7%; ±2 days, 93.1% vs 85.9%). Accuracy (±1 day) based on biparietal (BP) measurement was similar at week 5 and 6 of pregnancy (78.6% vs 78.9%; p > 0.05), whereas a significant decrease (p < 0.05) was observed at week 7 and 8 compared to week 6. No difference in the accuracy of the prediction at ±2 days based on BP was observed from week 5 to 8 of gestation (range from 82.3% to 95.2%). Close to term (week 9), the accuracies of the prediction based on BP were significantly lower than those obtained at week 5 (±1 day: 50.9% vs 78.6%, p < 0.05; ±2 days: 69.8% vs 95.2%, p < 0.005). The accuracy of the prediction in bitches and queens is influenced by the gestational period when ultrasonographic measurements are performed, particularly for BP measurement. Although a decrease in BP accuracy occurs along the pregnancy, the accuracy at ±1 and ±2 days of prediction of parturition term is highly consistent for 6 and 8 weeks of gestation, respectively.
Canine and feline pregnancy lasts approximately 9 weeks from the ovulation day, and a definitive diagnosis of pregnancy can be achieved only after 3 weeks in bitches and 2 weeks in queens (Concannon et al. 1983; Johnston et al. 2001).
It is well known that in bitches, the LH peak and initial rise of progesterone and ovulation occur, respectively, 65 and 63 (±1 day) before parturition (Concannon et al. 1983), but these data are not available when the oestrous cycle has not been monitored.
The LH concentration in queens increases with number of copulations and no concurrent rise of serum progesterone occurs (Johnston et al. 2001), making these prediction methods inapplicable.
The ultrasonographic identification and measurement of extrafoetal and foetal structures are the most accurate ways to predict the delivery day in the remaining 6–7weeks of pregnancy.
Among ultrasonographic parameters significantly related to gestational age in bitches and in queens, the inner diameter of chorionic cavity (ICC) is the most commonly used to predict the parturition day in early pregnancy (Zambelli et al. 2002; Luvoni and Beccaglia 2006). Specific equations for queens, small- and medium-size bitches are needed (Zambelli et al. 2002; Luvoni and Beccaglia 2006; Beccaglia et al. 2008), while a correction factor has been suggested for giant-size bitches (Kutzler et al. 2003).
Biparietal diameter (BP) is widely applied for the prediction of parturition day in the second half of pregnancy as the technical approach is relatively simple, and its growth is significantly correlated with gestational age (Luvoni and Beccaglia 2006; Beccaglia et al. 2008).
However, the reliability of the determination of gestational age might be influenced by the stage of embryo/foetal development. In clinical practice, it is crucial to know at what stage the ultrasonographic measurements of the aforementioned parameters provide the highest accuracy of the prediction of parturition term.
Accurate determination of the expected gestational term is needed for planning parturition assistance or elective caesarean section when the complete foetal maturation has occurred. Several other conditions require an accurate evaluation of foetal growth, such as high-risk pregnancies requiring therapeutic intervention, or over-term and pre-term labour that need a correct diagnosis (Lopate 2008).
Hence, the aim of this study was to investigate in bitches and queens whether the accuracy of parturition date prediction is affected by the week of pregnancy when the ultrasonographic examination is performed.
Materials and Methods
The accuracy of the prediction (±1 and ±2 days) using ICC and BP measurements was analysed retrospectively on the gestational period basis (from week 4 to 9 of pregnancy) in 495 ultrasonographic examinations of privately owned pregnant bitches (small-size bitches up to 10 kg and medium-size bitches from 10.5 to 30 kg) and in 60 of pregnant queens (3–5 kg).
The ultrasonographic examinations were performed with a SonoAce 8800 (Medison Co. Ltd., Seoul, Korea) equipped with a multi-frequency (5, 6.5, 7.5 MHz) microconvex probe.
Inner chorionic cavity was identified and measured at week 4 and 5, while BP was measured from week 5 to 9 of pregnancy.
The measurement of the ICC was determined by taking the mean value of the two transversal and orthogonal diameters from one side of the trophoblastic decidual reaction to the other. The BP was visualized on a longitudinal scan of foetal head, and the distance was recorded when the parietal bones were parallel. During the examination, the ICC and the BP were measured on a minimum of two different foetuses. The mean value of the data was calculated, and the predicted day of parturition was obtained by the application of the following equations previously described (Luvoni and Grioni 2000; Beccaglia et al. 2008):
ICC in small-size bitches: days before parturition =(mm – 68.68)/1.53;
ICC in medium-size bitches: days before parturition =(mm – 82.13)/1.8;
ICC in queens: days before parturition = (mm –62.03)/1.1;
BP in small-size bitches: days before parturition = (mm – 25.11)/0.61;
BP in medium-size bitches: days before parturition = (mm – 29.18)/0.7;
BP in queens: days before parturition = (mm – 23.39)/0.47)
The application of the equations mentioned above resulted in negative figures representing the number of days before parturition. The prediction was considered accurate when the difference between actual and predicted parturition dates was within ±1 day or ±2 days. The time of actual parturition was reported by the owners.
Mean (%) of accuracy at ±1 day or ±2 days was analysed by the chi-square test, and the level of significance was considered at p < 0.05.
Accuracy of the prediction of parturition on the gestational period basis is summarized in Table 1.
Table 1. Accuracy of parturition day prediction at different gestational ages in bitches and queens
|4||47/58 (81)a||–||54/58 (93.1)A||–|
|5||67/99 (67.7)a||33/42 (78.6)a,b||85/99 (85.9)A||40/42 (95.2)A|
|6||–||75/95 (78.9)a||–||84/95 (88.4)A|
|7||–||73/113 (64.6)b,c||–||93/113 (82.3)A,B|
|8||–||60/95 (63.2)b,c||–||81/95 (85.3)A|
|9||–||27/53 (50.9)c||–||37/53 (69.8)B|
In bitches and queens, the mean accuracy (±1 and ±2 days) of the prediction of parturition date obtained by the measurement of ICC was similar at week 4 and 5 of gestation.
At week 5 of pregnancy, when both structures were measurable, similar accuracies (±1 and ±2 days) were obtained with ICC and BP.
Accuracy (±1 day) based on BP measurement was similar at week 5 and 6 of pregnancy (p > 0.05), whereas a significant decrease (p < 0.05) was observed at week 7 and 8 compared to week 6. No difference in the accuracy of the prediction at ±2 days based on BP measurement was observed from week 5 to 8 of pregnancy.
Close to term (week 9), the accuracies (±1 and ±2 days) of the prediction based on BP diameter were significantly lower (p < 0.05 and p < 0.005) than those obtained at week 5.
In bitches and queens, the ultrasonographic visualization and measurement of extrafoetal and foetal structures allow the evaluation of gestational age and the prediction of the parturition term for an extended period of time (from week 4 to 9 of gestation).
This study demonstrates that the accuracy of the prediction is influenced by the gestational period when measurements are performed, particularly for BP.
We previously showed that ICC and BP are equally reliable parameters in obtaining a prediction of parturition date in the bitch in early and late pregnancy, respectively (Beccaglia and Luvoni 2006), but the overall accuracy was evaluated on bitch size basis and the accuracy in different gestational weeks was not considered.
Present data confirmed that in early pregnancy, the measurement of ICC leads to a high accuracy of the prediction. At week 4 of gestation, the embryonic vesicles appear regularly spherical with clearly defined margins and there is a low risk of inconsistent measurements of the two transversal diameters. In the following week, although the measurement is slightly influenced by the initial elongation of the chorionic cavity, the accuracy of the prediction is similar.
It is noteworthy that at this time (week 5), both parameters (ICC and BP) are equally accurate.
It has been reported that the estimation of gestational age in dogs is more precise during early pregnancy than afterwards (England et al. 1990; Kutzler et al. 2003; Kim et al. 2007), and in women, the measurement of the mean sac diameter is performed in the first trimester of pregnancy, but when the foetus is measurable, the crown-rump length is more accurate (Karki et al. 2006).
Kim et al. (2007) reported that the crown-rump length combined with body diameter measured between days 28 and 30 of canine gestation resulted in 87% of accuracy at ±2 days of the prediction of parturition term.
In a similar gestational period, the application of the formulae we previously described resulted in a high accuracy at ±2 days (ICC week 4, 93.1%; ICC week 5, 85.9%; BP week 5, 95.2%) suggesting that, as soon as the BP is visualized, its measurement provides reliable information on the gestational age and there is no need of combining multiple parameters.
Then, BP measurement maintains a high accuracy (±1 day) up to week 6 of pregnancy; afterwards, a gradual decrease is observed, thus maintaining a good accuracy at ±2 days until week 8.
Close to term (week 9), BP measurement is increasingly difficult because of the overlapping of multiple foetuses in the same ultrasonographic image field. Hence, inaccurate measurements might be responsible of the lowest accuracies observed (both ±1 and ±2 days).
The prediction of parturition term by BP measurement is not affected by the prevalence of one gender, but it is influenced by the number of foetuses (Beccaglia and Luvoni 2006). In pregnancies characterized by normal litter size (number of newborns within one standard deviation of the mean: small-size bitches – two to six pups and medium-size bitches – five to nine pups), the accuracy is higher than in pregnancies with small and large litters. The variability in growth rate is not recognizable in the early stages of embryo/foetal development, but becomes more evident approaching the final stages of gestation. Foetal overgrowth in small litters or undergrowth in large litters could decrease the accuracy of BP diameter close to term.
In humans, the measurement of foetal BP is performed not later than the second trimester of gestation, whereas in the third trimester, the head circumference or femoral length is preferable (Karki et al. 2006). However, in polytocous species such dogs and cats, some parameters, as femoral length, are less regularly visualized on the scan and measured less consistently than BP because of active movements of multiple foetuses.
In conclusion, the accuracy of the prediction term in bitches and queens changes on gestational week basis. The gestational period in which the examination is performed mostly affects the accuracy of the parameter that can be measured for an extended period of time, as BP (from week 5 to 9). Although a decrease in BP accuracy along the pregnancy occurs, the prediction of parturition term at ±1 and ±2 days is highly consistent for 6 and 8 weeks of gestation, respectively.
In the last week, other foetal structures should be examined with the aim of finding a suitable parameter to predict the parturition day because it is not uncommon in clinical practice to examine a bitch or a queen for the first time only few days before term.
Conflicts of interest
None of the authors have any conflicts of interest to declare.
Each of the authors contributed to the design and conduct of the research reported herein as original, and each contributed to the writing of the manuscript.