Although many bitches and queens deliver in the home or kennel/cattery setting without difficulty, requests for veterinary obstetrical assistance, including labour monitoring, are becoming more common. The increased financial and emotional value of stud dogs, brood bitches, toms, queens and their offspring to the pet fancy makes the preventable loss of even one neonate undesirable. Breeding colonies in academic, scientific and industrial facilities must maximise neonatal survival for financial and ethical reasons.
Veterinary involvement in canine and feline obstetrics has several goals:
- To increase live births, minimising the stillbirths that result from difficulties in the birth process
- To minimise morbidity and mortality in the dam
- To promote increased survival of neonates during the first weeks of life
Neonatal survival is directly related to the quality of labour. Optimal management of whelping and kittening requires an understanding of normal labour and delivery in the bitch and queen, as well as the clinical ability to detect abnormalities in labour. The latter is where advanced labour monitoring comes into play.
Eutocia is normal labour resulting in the vaginal delivery of viable neonates, whereas dystocia is defined as difficulty in the normal vaginal delivery of a neonate from the uterus. Dystocia must be diagnosed in a timely fashion for medical or surgical intervention to improve outcomes. Additionally, the aetiology of dystocia must be identified for veterinary personnel to make the best therapeutic decisions.
Optimal management of whelping and kittening requires an understanding of normal labour and delivery in the bitch and queen, as well as the clinical ability to detect abnormalities in labour
Physical examination should address the general status of the patient. It should include a digital and/or vaginoscopic pelvic exam for patency and contents of the birth canal, the evaluation of litter and foetal size (radiography is most useful for this) and the assessment of foetal viability (ideally using Doppler or real-time ultrasound) and uterine activity (tocodynamometry).
Labour and delivery
Stage I labour in the bitch normally lasts from 12 to 24 hours, during which time the uterus has myometrial contractions of increasing frequency and strength associated with cervical dilation. No abdominal effort (visible external contractions) is evident during stage I labour. Bitches can exhibit changes in disposition and behaviour during stage I labour, becoming reclusive or restless, nesting intermittently, refusing to eat and sometimes vomiting. Panting and trembling may also occur. At this stage, vaginal discharge is clear and watery.
We define normal stage II labour in the bitch as beginning when external abdominal efforts can be seen – these efforts normally accompany myometrial contractions to culminate in the delivery of a neonate. Presentation of the foetus at the cervix triggers the Ferguson reflex, promoting the release of endogenous oxytocin from the hypothalamus. Typically, these efforts should not last longer than one to two hours between puppies, although great variation exists between individuals. The entire delivery can take between 1 and 24 hours; however, normal labour is associated with shorter total delivery time (under eight hours) and shorter intervals between neonatal births (one hour). Vaginal discharge can be clear, serous to haemorrhagic, or green (uteroverdin). Typically, bitches continue to nest between deliveries and may nurse and groom neonates intermittently. Anorexia, panting and trembling are common.
Stage III labour is defined as the delivery of the placenta. Bitches typically vacillate between stages II and III of labour until the delivery is complete. During normal labour, all foetuses and placentae are delivered vaginally, although they may not be delivered together in every instance.
The stages of labour in the queen can be similarly defined. Stage I labour in the queen is reported to last 4 to 24 hours, and stages II and III between 2 and 24 hours.
Aetiology of dystocia
Dystocia results from maternal factors (uterine inertia, pelvic canal anomalies, intrapartum compromise), foetal factors (oversize, malposition, malposture, anatomical anomalies) or a combination of both.
Uterine inertia is the most common cause of dystocia. Primary uterine inertia results in the failure to deliver any neonates at term. It is thought to be multifactorial, including metabolic defects at the cellular level. An intrinsic failure to establish a functional, progressive level of myometrial contractility occurs, and a genetic component may be present. Secondary uterine inertia results in the cessation of labour once initiated and the consequential failure to deliver the entire litter. Secondary inertia can result from metabolic or anatomical (obstructive) causes and is also thought to have a genetic component.
Birth canal abnormalities such as vaginal strictures, stenosis from previous pelvic trauma or particular breed conformation, and intravaginal or intrauterine masses can cause obstructive dystocia. In most cases, canal abnormalities can be detected during the pre-breeding examination and resolved or avoided by elective caesarean section.
In most cases, canal abnormalities can be detected during the pre-breeding examination and resolved or avoided by elective caesarean section
Causes of intrapartum compromise, rendering the dam unable to complete delivery, include metabolic abnormalities such as hypocalcaemia and hypoglycaemia, systemic inflammatory reaction, sepsis and hypotension (due to haemorrhage or shock).
Foetal factors contributing to dystocia most commonly involve a mismatch of foetal and maternal size, foetal anomalies and foetal malposition and/or malposture. Prolonged gestation with a small litter size can cause dystocia due to an oversized foetus(es). Similarly, foetal anomalies, such as hydrocephalus and anasarca, can cause dystocia. Foetal malposition (ventrum of foetus proximal to the dam’s dorsum) and foetal malposture (flexed neck and scapulohumeral joints most commonly) promote dystocia, as the foetus cannot traverse the birth canal smoothly.
Veterinary obstetrical monitoring – a novel approach
A novel approach to veterinary obstetrical monitoring, which is in use in the United States, involves external monitoring devices that use digital tocodynomometry and a handheld Doppler to detect and record uterine activity and foetal heart rates (Veterinary Perinatal Services (VPS), Wheat Ridge, USA). These devices can be used either in the home setting or at the veterinary clinic.
Use requires the hair coat to be lightly clipped caudal to the ribcage, over the gravid area of the lateral flanks, to allow proper contact of the uterine sensor and foetal Doppler. The uterine sensor (Figure 1), which detects changes in intrauterine and intra-amniotic pressures, is strapped over the lightly clipped area of the bitch or queen’s caudolateral abdomen using an elasticised strap, with the sensor’s recorder nearby (Figure 2).
During labour monitoring sessions, the bitch or queen is at rest in the whelping/kittening box or a crate/cage, or held by the owner or nurse. The monitoring equipment is well tolerated. Foetal Doppler monitoring is performed bilaterally with a handheld unit with the bitch or queen in lateral recumbency, using acoustic coupling gel. Directing the Doppler perpendicularly over a foetus results in a characteristic amplification of the foetal heart sounds, distinct from maternal arterial or cardiac sounds, which enables the determination of foetal heart rates. This can also be performed with ultrasound.
Interpreting data
Uterine data (Figure 3) is transferred digitally 24/7 to VPS obstetrical personnel for interpretation, who subsequently consult with the attending veterinarian and client, enabling management with insight. Clinicians do not need to become competent at evaluating the data strips from labour monitoring sessions.
The canine and feline uterus have characteristic normal patterns of contractility, varying in frequency and strength before and during different stages of labour. During stages I and II of labour, uterine contractions vary in frequency from 0 to 12 per hour, and in strength from 15 to 40mmHg, with spikes up to 60mmHg. Contractions during active labour can be from two to five minutes in duration.
Recognisable patterns exist during pre-labour and active (stages I to III) labour (Figure 4). Aberrations in uterine contractility can, therefore, be detected (Figure 5). Abnormal, dysfunctional patterns can be weak or prolonged, often associated with foetal distress detected by Doppler or ultrasound. Additionally, the completion of labour (or lack thereof) can be evaluated via tocodynomometry.
The presence of foetal distress is reflected by sustained deceleration of heart rates. Normal canine and feline foetal heart rates at term are from 170 to 230bpm. Brief decelerations can occur during contractions. Prolonged deceleration associated with uterine contractions suggest mismatch in size between the foetus and dam, or foetal malposition or malposture. Transient accelerations occur with normal foetal movement. Foetal heart rates of 150 to 160bpm or lower indicate stress. Foetuses with heart rates of 130bpm or lower have poor survival if not delivered promptly, and foetuses with heart rates lower than 100bpm are an indication for immediate intervention to hasten delivery (medical or surgical) before their demise.
