Gestation Aging
Now available on iTunes App Store.
The Gestation Aging App was developed at the University of Wisconsin School of Veterinary Medicine by Drs. C. Checura and H. Momont and Mr. T. Bennett.
The app uses a series of inputs made by the user to estimate the approximate age of the pregnancy based on ultrasonographic measurements.
Disclaimer
This app is intended for educational and entertainment purposes only. Do not rely on information derived here to make clinical decisions about any pregnant animal. Induction of labor and elective caesarean section are major medical procedures that should only be performed in the context of a valid veterinary-client-patient relationship (VCPR). The predictions in this app do not necessarily account for all variation due to breed differences within the species listed, individual animal variation (dam or fetus), operator error, or measurement bias. Many of the predictive equations are linear approximations of growth parameters that are not strictly linear. And finally, gestation lengths used in this app are commonly recognized species standards but breed and individual animal variation exists here as well and this is an especially significant source of variability in those species with long gestation periods.
Measurement Options
A variety of measurement options are available in this app but not all are created equal. As a very general rule, embryonic vesicle (EV) height, abdominal measures (TD, AD, AH) and biparietal diameter (BPD) are the more accurate methods for staging gestation in most species. In later gestation, eye length is usually the most readily accessible measure but all techniques are subject to large error as the pregnancy advances and should be interpreted with caution.
As a general rule, when staging gestation in litter bearing species, all measures should be made on two or more fetuses and the resulting values averaged.
In the mare, the early growth profile of the embryonic vesicle (EV) is distinctly non-linear so measurement of the EV alone is a poor method of staging early equine gestation.
Biparietal diameter (BPD) is the width of the skull directly behind the orbit and is typically measured as the widest point of the skull in a symmetrical view. It is also referred to as head or skull width/diameter.
Crown rump length (CRL) refers to the distance from the top of the head to the base of the tail. This is typically the longest linear dimension of the fetal image. An obvious limitation of this measure in predicting age by ultrasound is the length of linear array probes. Sector probes can extend the useful diagnostic window but this measure is still limited to the first trimester for large animals.
Amniotic vesicle (AV) diameter is the measure of the amniotic sac immediately surrounding ruminant fetuses. As the fetus lengthens during the second month of gestation, the amnion becomes dramatically longer in comparison to its width and an attempt should be made to measure the greatest dimension.
Eye length (EL) is the linear measure of the long axis of the orbit. The eye becomes progressively more ovoid in later gestation.
Head length (HL) is the distance from the poll to the tip of the nose.
Trunk diamter (TD), abdominal diameter (AD) and abdominal height (AH) are measured at the level of the umbilical attachment.
Thoracic height (TH) is measured at the level of the heart.
Getting Started
When the app is initiated, the user is presented with multiple text fields in which to enter data. All data entry is handled by choosing an option within the pick list.
Species, animal type and measurements:
The species represented in this app include Bovine (Cow), Ovine (Sheep), Caprine (Goat), Camelid (Alpaca, Llama, Camel), Equine (Horse), Cervine (Deer), Bubaline (Buffalo), Canine (Dog), Feline (Cat) and Porcine (Swine). Within some species (Caprine, Camelid, Cervine and Canine), a list of animal types is offered. Each species has its own set of measured items used to assess the age of the fetus. These include:
| Measurement | Example Picture |
|---|---|
| AD (abdominal diameter)
Diameter of the abdomen |
 |
| AH (abdominal height)
Height of the abdomen |
 |
| AV (amniotic vesicle diameter)
The measure of the amniotic sac immediately surrounding ruminant fetuses. |
 |
| BPD (biparietal diameter)
Width of the skull directly behind the orbit. |
 |
| CRL (crown rump length)
Distance from the top of the head to the base of the tail. |
 |
| EL (eye length)
Linear measure of the long axis of the orbit |
 |
| EV (embryonic vesicle height)
The entirety of the fluid component of the spherical fetal compartment |
 |
| HL (head length)
Distance from the poll to the tip of the nose. |
 |
| TD (trunk diameter)
Trunk diameter measured at the level of the umbilical attachment |
 |
| TH (thoracic height)
Chest height measured at the level of the heart. |
 |
Each measurement has minimum and maximum values represented at the extremes of the picklist.
Gestation age in days is either calculated based on formulas or derived from look up tables. The days to parturition is calculated using the average accepted gestation length and subtracting the gestation age. Also included is a +/- value to illustrate the normal range of gestation length.
Gestation Ageing Measurements
| Measurement | Min. Meas. | Max. Meas. | Min. GA | Max. GA |
|---|---|---|---|---|
| Bovine (Cow) | ||||
| AV | 7 | 14 | 26 | 36 |
| BPD | 17 | 84 | 56 | 131 |
| CRL | 17 | 184 | 34 | 75 |
| HL | 27 | 144 | 62 | 132 |
| TD | 17 | 124 | 54 | 132 |
| Measurement | Min. Meas. | Max. Meas. | Min. GA | Max. GA |
|---|---|---|---|---|
| Ovine (Sheep) | ||||
| AH | 18 | 85 | 50 | 120 |
| BPD | 15 | 50 | 47 | 119 |
| TH | 20 | 75 | 50 | 119 |
| Measurement | Min. Meas. | Max. Meas. | Min. GA | Max. GA |
|---|---|---|---|---|
| Caprine (Goat) | ||||
| Angora | ||||
| BPD | 8 | 41 | 43 | 101 |
| Nubian | ||||
| BPD | 8 | 42 | 41 | 100 |
| Pygmy | ||||
| BPD | 8 | 37 | 40 | 101 |
| Toggenburg | ||||
| BPD | 8 | 44 | 41 | 100 |
| Dairy breeds | ||||
| BPD | 8 | 40 | 40 | 101 |
| Measurement | Min. Meas. | Max. Meas. | Min. GA | Max. GA |
|---|---|---|---|---|
| Camelid (Alpaca, Llama, Camel) | ||||
| Alpaca | ||||
| BPD | 1.0 | 7.0 | 42 | 325 |
| TH | 1.0 | 6.5 | 34 | 324 |
| Bactrian Camel | ||||
| BPD | 1.0 | 3.1 | 57 | 105 |
| CRL | 0.6 | 4.5 | 23 | 65 |
| EL | 0.5 | 1.3 | 68 | 126 |
| Dromedary Camel | ||||
| BPD | 1.0 | 3.1 | 57 | 105 |
| CRL | 0.6 | 4.5 | 23 | 65 |
| EL | 0.5 | 1.3 | 68 | 126 |
| Llama | ||||
| BPD | 1.0 | 8.0 | 43 | 344 |
| TH | 1.0 | 7.0 | 44 | 325 |
| Measurement | Min. Meas. | Max. Meas. | Min. GA | Max. GA |
|---|---|---|---|---|
| Equine (Horse) | ||||
| EL | 10 | 37 | 86 | 318 |
| EV | 4 | 56 | 9 | 45 |
| Measurement | Min. Meas. | Max. Meas. | Min. GA | Max. GA | |
|---|---|---|---|---|---|
| Cervine (Deer) | |||||
| Red deer | |||||
| BPD | 7 | 42 | 42 | 127 | |
| CRL | 7 | 61 | 25 | 59 | |
| EL | 3 | 30 | 55 | 154 | |
| HL | 8 | 46 | 44 | 83 | |
| Whitetail | |||||
| CRL | 6 | 60 | 23 | 59 | |
| Elk | |||||
| CRL | 6 | 60 | 23 | 59 | |
| Fallow | |||||
| CRL | 38 | 192 | 54 | 117 | |
| EL | 5 | 17 | 54 | 126 | |
| HL | 16 | 85 | 54 | 124 | |
| Measurement | Min. Meas. | Max. Meas. | Min. GA | Max. GA |
|---|---|---|---|---|
| Bubaline (Buffalo) | ||||
| AV | 13 | 31 | 36 | 57 |
| BPD | 12 | 58 | 59 | 138 |
| CRL | 9 | 43 | 28 | 70 |
| Measurement | Min. Meas. | Max. Meas. | Min. GA | Max. GA |
|---|---|---|---|---|
| Canine (Dog) | ||||
| Small breeds | ||||
| BPD | 4 | 28 | 27 | 63 |
| CRL | 4 | 40 | 29 | 40 |
| Medium breeds | ||||
| BPD | 4 | 29 | 26 | 63 |
| CRL | 4 | 44 | 28 | 40 |
| Large breeds | ||||
| BPD | 4 | 30 | 24 | 63 |
| CRL | 4 | 50 | 26 | 40 |
| Measurement | Min. Meas. | Max. Meas. | Min. GA | Max. GA |
|---|---|---|---|---|
| Feline (Cat) | ||||
| AD | 13 | 38 | 31 | 60 |
| BPD | 11 | 25 | 30 | 60 |
| Measurement | Min. Meas. | Max. Meas. | Min. GA | Max. GA |
|---|---|---|---|---|
| Porcine (Swine) | ||||
| CRL | 20 | 85 | 29 | 48 |