Malignant pleural mesothelioma: clinical experience and prognostic value of derived neutrophil-to-lymphocyte ratio and PD-L1 expression.

BACKGROUND: Malignant pleural mesothelioma (MPM) is a rare and aggressive tumor, with a poor prognosis. MPM needs to find prognostic factors of survival. We provided the management of patients with MPM and sought to determine whether pre-treatment levels of derived neutrophil-to-lymphocyte ratio (dNLR) as well as PD-L1 expression were reliable prognostic factors of survival. METHODS: We conducted a single-institution retrospective study, including all patients with MPM treated at La Paz University Hospital between December 2009 and March 2018. Baseline disease, demographics, clinical data, treatment characteristics and complete blood cell counts were collected. We examined dNLR at baseline and data for PD-L1 expression were analyzed in tumor cells by immunohistochemistry. RESULTS: We included 25 patients. The median overall survival (OS) was 15.7 months (95% CI 11.3-20.0). 5 patients had a dNLR greater than 3 (20%). Patients with a dNLR greater than 3 had shorter median OS (8.5 months), than patients with a dNLR less than 3 (17.0 months), with statistically significant differences (p = 0.038). Ten patients (40%) had positive PD-L1 expression (≥ 1%). Patients with positive PD-L1 expression had shorter median OS (8.5 months) than patients with negative PDL1 expression (15.7 months), but without statistically significant association (p = 0.319). CONCLUSION: The survival data obtained in our sample are consistent with those previously reported. Pretreatment levels of dNLR greater than 3 and positive PD-L1 expression could be significant prognostic factors for poor survival in patients with MPM. Further and prospective studies are needed to explore this relationship and to derive definitive conclusions.

Prevención de extubación no programada en pacientes con ventilación mecánica invasiva / Prevention of non-programed tube-extractions among patients with invasive mechanical ventilation / Prevenção de extubação não programada em pacientes com ventilação mecânica invasiva

Introducción Las extubaciones no programadas constituyen un evento adverso frecuente y de alto impacto, en la mayoría de los casos la presencia de este evento se relaciona con factores como la vía aérea, ventilación mecánica, nivel de sedación, estado y actividad mental del paciente, entre otros también prevenibles. Por ello, se establece un indicador de calidad para prevenir extubaciones no programadas en pacientes con ventilación mecánica invasiva y tubo endotraqueal. Objetivo Realizar la validación de contenido del indicador y describir el nivel de cumplimiento para la prevención de extubaciones no programadas en pacientes con ventilación mecánica invasiva en un hospital de tercer nivel de la Ciudad de México, con el propósito de dar a conocer nuevos aportes en materia de prevención. Metodología Estudio cuantitativo y descriptivo, con una muestra no probabilística a conveniencia conformada por 46 procesos observados durante el turno matutino en tres servicios de hospitalización. Resultados Se encontró que el 96% de los procesos observados arrojaron un nivel de prevención medio para las extubaciones no programadas. Al evaluar el índice de eficiencia global del indicador, se obtuvo un resultado del 59.8%, lo cual muestra que las acciones para prevenir una extubación no programada se cumplen en un porcentaje muy bajo. Conclusiones Se detectó una omisión de funciones por los profesionales de la salud en la prevención de este evento, por lo que se propuso un plan de mejora para la institución con el propósito de disminuir los eventos relacionados a las extubaciones.

Introduction Non-programed extubation, constitute a frequent high impact adverse event involving issues on the airway, mechanical ventilation, sedation level, patient´s mental activity, among others. Because of this, a quality indicator is established in order to help prevent non-programed extubation among patients with invasive mechanical ventilation and endotracheal tube. Objective To perform a validation of content on this indicator in a third level hospital of the City of Mexico, and describe the level of adherence to its components in order to prevent non-programed extubation among patients with invasive mechanical ventilation and endotracheal tube, and share the resulting contributions in the area of prevention. Methodology This is a quantitative and descriptive study with a non-probabilistic sample by convenience of 46 processes which were observed during the morning shifts in three hospitalization services. Results It was found that 96% of the processes observed showed an insufficient level of prevention of non-programed extubation. The assessment of the efficiency related to indicator´s components showed a 59.8% compliance, suggesting that the actions to prevent non-programed extubation are not sufficiently taken. Conclusions An important related omission by health professionals regarding the prevention of this kind of adverse events was detected, and thus, a corresponding improvement plan for the institution was proposed.

Introdução As extubaçãos não programadas constituem um evento adverso frequente e de alto impacto, na maioria dos casos, a presença deste evento relaciona-se com fatores como a via aérea, ventilação mecânica, nível de sedação, estado e atividade mental do paciente, entre outros, também preveníeis. Por isso, estabelece-se um indicador de qualidade para prevenir extubaçãos não programadas em pacientes com ventilação mecânica invasiva e tubo endotraqueal. Objetivo Realizar a validação de conteúdo do indicador e descrever o nível de cumprimento para a prevenção de extubaçãos não programadas em pacientes com ventilação mecânica invasiva em um hospital de terceiro nível da Cidade do México, com o propósito de dar a conhecer novas contribuições em matéria de prevenção. Metodologia Estudo quantitativo e descritivo, com uma amostra não probabilística a conveniência, conformada por 46 processos observados durante o turno matutino em três serviços de hospitalização. Resultados Encontrou-se que o 96% dos processos observados revelaram um nível de prevenção médio para as extubaçãos não programadas. Avaliando o índice de eficiência global do indicador, obteve-se um resultado do 59.8%, o qual mostra que as ações para prevenir uma extubação não programada cumprem-se em uma porcentagem muito baixa. Conclusões Identificou-se uma omissão de funções pelos profissionais da saúde na prevenção deste evento, pelo que se propus um plano de melhora para a instituição com o propósito de diminuir os eventos relacionados às extubaçãos.

Absence of toxicity and genotoxicity in an extract of Rubus coriifolius.

Rubus coriifolius Focke is a wild plant from the Rosaceae family. It grows in both Guatemala and Mexico. The polar extract of the aerial parts of this plant has antibacterial, anti-inflammatory, and anti-protozoal activities. These properties may explain the traditional use of this plant. In vivo and in vitro assays were used to assess the genotoxic and toxic effects of an ethanol extract of the aerial parts of R. coriifolius. Three groups of rats were orally administered the R. coriifolius extract diluted in ethanol (5%) at doses of 1.89 mg/kg body weight (low dose), 4.72 mg/kg body weight (medium dose), and 9.44 mg/kg body weight (high dose) for 3 weeks. Genotoxic/cytotoxic effects induced by the R. coriifolius ethanol extract were evaluated in vivo by a micronuclei (MN) test in rat's bone marrow cells and in vitro by MN and sister chromatid exchange (SCE) in human lymphocyte cultures. In vivo genotoxicity analyses revealed that the average number of micronucleated polychromatic erythrocytes and the polychromatic erythrocyte/red blood cell ratio at all doses were not significantly different from those of the negative control. In vitro genotoxicity analyses showed that MN, SCE, and proliferative index frequencies in a human lymphocyte cell culture were not significantly different from those of the negative control. These results demonstrate that the ethanol extract of R. coriifolius aerial parts is not toxic or mutagenic (in vitro and in vivo) and does not affect cell proliferation at the concentrations analyzed.

Digital image analysis of AgNORs in cervical smears of women with premalignant and malignant lesions of the uterine cervix.

We performed a hospital-based, unmatched case-control study to investigate the association between progressive stages of cervical neoplasia and digital analysis of cell proliferation by silver stained nucleolus organizer region associated proteins (AgNORs). We measured cell proliferation levels in the cervical epithelial cells of 10 women with low grade squamous intraepithelial lesions (LG-SIL), eight with high grade squamous intraepithelial lesions (HG-SIL), 11 with cervical cancer (CC) and eight with no cervical lesions (controls) using the AgNORs technique. Cell proliferation was measured by digital image analysis (DIA). DIA revealed increased total areas of AgNORs in HG-SIL and CC compared to LG-SIL and control patients. AgNORs with a kidney or cluster shape exhibited greater areas than those with a spherical or long shape. We propose a cut-off of 118 pixels to differentiate benign (control and LG-SIL) from malignant (HG-SIL and CC) lesions. DIA of AgNORs is a simple and inexpensive method for studying proliferation. The increased total area of AgNORs in malignant lesions provides information regarding cell behavior and may be related to cervical carcinogenesis; however, further validation studies are required to establish its usefulness in cytological analysis.

Localisation and quantification of alkali-labile sites in human spermatozoa by DNA breakage detection-fluorescence in situ hybridisation.

The localisation and quantification of constitutive alkali-labile sites (ALSs) were investigated using a protocol of DNA breakage detection plus fluorescence in situ hybridisation (DBD-FISH) and alkaline single-cell gel electrophoresis (SCGE or comet assay), in spermatozoa of infertile and fertile men. Semen samples from 10 normozoospermic patients undergoing infertility treatment and 10 fertile men were included in this study. ALSs were localised and quantified by DBD-FISH. The region most sensitive to alkali treatment in human spermatozoa was located in the basal region of the head. ALSs were more frequent in spermatozoa of infertile men than in those of fertile men. These results were confirmed by SCGE comet assays. In conclusion, the most intense localisation of hybridisation signals in human spermatozoa, representing the highest density of constitutive ALSs, was not randomly distributed and was predominantly located in the base of the head. Moreover, infertile men presented with an increase in ALS frequency. Further studies are necessary to determine the association between ALS, sperm chromatin organisation and infertility.

Total homocysteine levels in healthy children from the Monterrey metropolitan area, Mexico.

Currently, there are indications for determining hyperhomocysteinemia in adulthood as risk factors for cardiovascular diseases, psychiatric disorders, pregnancy complications, birth defects, cognitive impairment in the elderly, in addition to cancer. If hyperhomocysteinemia is determined from childhood, it may be modulated with the provision of an opportunity for public health intervention. The objective of this descriptive study was to determine total homocysteine (tHcy) levels in healthy children from the Monterrey metropolitan area in Mexico. In a peripheral-blood sample collected from 56 healthy children aged 2-10 years, we determined tHcy concentration by high performance liquid chromatography (HPLC) with fluorescence detection. The geometric mean +/- SD was 9.78 +/- 1.73 micromol/l. tHcys of the children studied were homogeneous by age cohort and gender. Nutritional state was classified by body mass index (BMI). Sixty five percent of children who participated in the study had normal BMI, and 96% of the children belong to the low socioeconomic status. In conclusion, to our knowledge this is the first-ever information on homocysteine (Hcy) prevalence in a population of healthy Mexican children. tHcy concentration was higher than that reported in other populations studies. This preliminary study could constitute the baseline for future public health studies.

Frecuencia y carga viral relativa del virus del papiloma humano de alto riesgo según el diagnóstico citológico en mujeres paraguayas por captura híbrida II / Frequency and relative viral load of high risk human papilloma virus according to the cytological diagnosis in paraguayan women by hybrid capture II

El cáncer de cuello uterino es el tumor maligno más frecuente en mujeres de Latinoamérica y su agente causal es el virus del papiloma humano (HPV). Recientemente en Paraguay incorporamos el método de captura híbrida II (CH II), el cual detecta 13tipos de HPV de alto riesgo oncogénico (HR-HPV) y proporciona valores relativos de carga viral. El objetivo del estudio fue determinar la carga viral relativa de HR-HPV por CH IIsegún el diagnóstico citológico. Fueron incluidas 566 mujeres (33 + 10 años) atendidas en el Instituto de Investigaciones en Ciencias de la Salud 2006/2009. Fue detectado HRHPVen 43% de las mujeres (241/566), observándose una alta frecuencia del 23% en mujeres con ausencia de lesión intraepitelial (NSIL). Según el diagnóstico citológico, se evidenció una diferencia altamente significativa entre los valores de carga viral relativa(p<0,0001; Kruskal Wallis), observándose un aumento de carga viral relativa de mujeres con NSIL a mujeres con SIL (68 pg/ml en ausencia de SIL; 710 pg/ml para SIL de bajo grado-LSIL y 474 pg/ml para SIL de alto grado-HSIL). No se observó cambio significativo en la carga viral relativa entre LSIL y HSIL (p=0,60; prueba t de Student). Los resultados sugieren que los valores de carga viral relativa proporcionados por CH II pueden ser considerados como un indicador importante en el manejo de mujeres con sospecha de SIL.

Cervical cancer is the most frequent malignant tumor in women of Latin America being human papillomavirus (HPV) the main causative agent. Recently in Paraguay, we incorporated the method of hybrid capture II (CH II) which detects 13 types of HPV ofhigh oncogenic risk (HR-HPV) and provides relative values of viral load. The aim of this study was to determine the frequency and relative viral load of HR-HPV by CH II according to the cytological diagnosis. There were 566 women (33 + 10 years) included in the study that attended the Research Institute in Health Sciences during the period 2006/2009. HR-HPV was detected in 43% of the women (241/566), being observed a high frequency of 23% in women negative to squamous intraepithelial lesions (NSIL). According to the cytological diagnosis, there was a highly significant difference between the values of relative viral load (p <0.0001; Kruskal Wallis), with an increase of relative viral load of women with NSIL to women with SIL (mean values: 68 pg/ml in NSIL; 710 pg/ml in low grade SIL-LSIL and 474 pg/ml in high grade SIL-HSIL). Significant change was not observed in the relative viral load between LSIL and HSIL (p=0.60; Student’s t test).The results suggest that the values of relative viral load provided by CH II could be considered an important indicator for managing women with suspicion of SIL.

Poly(ADP-ribose)polymerase-1 (PARP-1) in carcinogenesis: potential role of PARP inhibitors in cancer treatment.

Poly(ADP-ribose)polymerase-1 (PARP-1) is a nuclear, zinc-finger, deoxyribonucleic acid (DNA)-binding protein that detects specifically DNA strand breaks generated by different genotoxic agents. Whereas activation of PARP-1 by mild genotoxic stimuli facilitates DNA repair and cell survival, severe DNA damage triggers different pathways of cell death, including PARP-mediated cell death through the translocation of apoptosis inducing factor (AIF) from the mitochondria to the nucleus. Pharmacological inhibition or genetic ablation of PARP-1 results in a clear benefit in cancer treatment by different mechanisms, including selective killing of homologous recombinationdeficient tumor cells, downregulation of tumor-related gene expression, and decrease in the apoptotic threshold in the cotreatment with chemo- and radiotherapy. We summarize in this review the findings and concepts for the role of PARP-1 and poly(ADP-ribosylation) in the regulation of carcinogenesis and some of the preclinical and clinical data available for these agents, together with the challenges facing the clinical development of these agents.

DNA fragmentation in frozen sperm of Equus asinus: Zamorano-Leonés, a breed at risk of extinction.

The dynamics of sperm DNA fragmentation (sDF) and sperm viability were analyzed in frozen-thawed sperm samples of Equus asinus (Zamorano-Leonés), a breed at risk of extinction. Sperm DNA fragmentation was assessed using an adaptation of the sperm chromatin dispersion test developed for stallions in five different frozen samples. Sperm were thawed and incubated at different temperatures (37 degrees C, 25 degrees C, and 4 degrees C) and sDF was assessed at different times and compared. The mean sDF after thawing at the beginning of the experiment was 18.20+/-14.77% and did not differ significantly from the results of a neutral comet assay (22.0+/-19.34%). The tendency in the sDF of all donkeys indicated that sperm DNA is more sensitive to breakage when incubated at 37 degrees C than when incubated at 25 degrees C or 4 degrees C. Interestingly, the tendency was not the same when different animals were compared, and differences in sDF dynamics were established among individuals. sDF correlated negatively with sperm viability in some individuals but not in others. From a conservation perspective, sDF analysis may offer a new way to assess sperm quality in endangered breeds in order to identify and select the best semen samples for artificial reproduction purposes. In particular, we recommend for artificial insemination the use of semen samples with a slow increase in sDF with time after thawing.

Frequency of micronuclei in Mexicans with type 2 diabetes mellitus.

A case-control study was carried out on a sample of 15 Mexican patients (40-56 years old) with type 2 diabetes mellitus (DM2) that had developed five years and been treated with oral hypoglycemic drugs (sulfonylurea and/or metformin), with no microvascular or macrovascular complications. The aim of this study was to assess whether Mexican patients with DM2 differed from a control group in the frequency of micronuclei (MN). A control group of 10 individuals without DM2 (38-54 years old) was included. The frequency of MN in binucleated lymphocytes was analyzed according to the Fenech criteria. At time being this investigation should be considered as a preliminary study in which the influence of potential confounders cannot be adequately assessed. However, our result showed a MN frequency significant increase in DM2 patients (6.53 +/- 2.03 per 1000 cells) relative to that of the control group (3.10 +/- 1.79 per 1000 cells). MN may constitute a possible component of a panel of biomarkers for the risk of DM2. This cytogenetic damage also indicates an enhanced risk of cancer, as has been found in previous studies. These results should be validated by other researchers.

Propuesta metodológica de auditoria de efluentes líquidos en las pequeñas y medianas industrias (PYMES) que descargan en cuerpos de agua con condiciones particulares de descarga (CPD’s)

El informe final elaborado por la representante mexicana al curso regional propone una metodología de auditoria para ser aplicada a los efluentes líquidos de pequeñas y medianas empresas que descargan sus efluentes a cuerpos receptores con el objeto de disminuir dichas descargas

Propuesta metodológica de auditoria de efluentes líquidos en las pequeñas y medianas industrias (PYMES) que descargan en cuerpos de agua con condiciones particulares de descarga (CPDs)

El informe final elaborado por la representante mexicana al curso regional propone una metodología de auditoria para ser aplicada a los efluentes líquidos de pequeñas y medianas empresas que descargan sus efluentes a cuerpos receptores con el objeto de disminuir dichas descargas

Biocontrol of Bacillus subtilis against Fusarium verticillioides in vitro and at the maize root level.

Bacillus species as a group offer several advantages over other bacteria for protection against root pathogens because of their ability to form endospores, and because of the broad-spectrum activity of their antibiotics. The objectives of this work were to determine the ability of strains of Bacillus to inhibit Fusarium verticillioides growth and fumonisin B(1) accumulation in vitro, and to evaluate the ability of the best bacterium for preventing rhizosphere and endorhizosphere colonization by F. verticillioides. Bacterial populations from the maize rhizoplane were obtained, and the capacity of ten Bacillus strains to inhibit fungal growth and fumonisin B(1) accumulation in vitro was assayed. According to these results, B. subtilis CE1 was selected as the best antagonist for testing maize root colonization of F. verticillioides. Bacillus subtilis CE1 at 10(8) and 10(7) CFU ml(-1) inocula was able to reduce rhizoplane and endorhizosphere colonization of F. verticillioides in greenhouse trials. The strain B. subtilis CE1 could be a potential biological control agent against F. verticillioides at the root level.

Type 2 diabetes mellitus among youth in Puerto Rico, 2003

AIMS: To describe the clinical characteristics, and estimate the prevalence of type 2 diabetes mellitus among Puerto Rican youth, 1995-2003. METHODS: All patients aged less than 20 years with a confirmed diagnosis of type 2 diabetes were identified from pediatric endocrinologists' medical practices. Medical records of each patient were reviewed to confirm the diagnosis, classify the type of diabetes, and gather sociodemographic and clinical characteristics. From 1995 to 2003 a total of 32,444 records were reviewed. A total of 2,800 children with diabetes were identified, of which 2,702 were type 1 and 93 type 2; typel/type 2 ratio was 29:1. Frequency distributions were obtained for categorical variables, and summary measures (mean +/- standard deviation) for quantitative measure were computed. RESULTS: Mean age at first visit was 14 years. The majority of cases were females (69), for a female/ male ratio of 2.2:1. 78.5had a family history of the disease, 74.2were overweight, and 48had acanthosis nigricans. 64.5of the cases were receiving some type of hypoglycemic therapy. 18.5of the cases had severe hypertension while 17.5had cholesterol levels considered at increased risk (e[quot ]200). The overall prevalence was 13.5 per 100,000 population. CONCLUSIONS: This study is the first that describes the frequency and clinical presentation of type 2 diabetes in children and adolescents in a sample of Puerto Ricans. Further investigations must be conducted to obtain a more precise estimate of the burden of type 2 diabetes in youth and to raise awareness of this condition among health care professionals.

Chromosomal abnormalities and polymorphisms in Mexican infertile men.

A cross-sectional study was conducted to estimate the prevalence of chromosome abnormalities and normal variable chromosome features (polymorphisms) in infertile men from northeastern Mexico. Karyotyping was carried out in 326 men with diagnosis of infertility. The sperm counts showed 204 patients with oligozoospermia, 87 with azoospermia and 35 normozoospermia. Five patients with oligozoospemia and two with azoospermia presented chromosome abnormalities. Nonzoospermic men did not show chromosomal abnormalities. Polymorphisms of heterochromatin and satellite length showed a significant increased in oligozoospermic and azoospermic men with respect to normozoospermic men, respectively. This study reports the prevalence of chromosome abnormalities, polymorphisms of heterochromatin length, and polymorphisms in satellites in Mexican infertile men. The prevalence in this study was similar to other studies in world literature.

Immunodiagnosis of fasciolosis using recombinant procathepsin L cystein proteinase.

Cathepsin L1, a cysteine protease secreted by the gastrodermis of juvenile and adult Fasciola hepatica, was expressed in Escherichia coli as a fusion protein containing the proregion, supplied with six histidyl residues at the N-terminal end (rproCL1). In this study we tested its potential as antigen for the serologic diagnosis of F. hepatica infections by enzyme-linked immunosorbent assay (ELISA). The analyzed human sera included 16 positive samples, 99 negative controls and 111 from individuals affected by other parasitic and non parasitic diseases. The sensitivity and specificity of the rproCL1-ELISA were 100%. We also assessed the ability to detect antibodies in sera from 10 experimentally infected sheep, obtaining preliminary results that shown a response since the third week post infection in all the studied animals. Therefore, the recombinant rproCL1-based ELISA could be a standardized test for the accurate diagnosis of fasciolosis.

Immunodiagnosis of human fascioliasis by an enzyme-linked immunosorbent assay (ELISA) and a micro-ELISA.

Enzyme-linked immunosorbent assay (ELISA) and micro-ELISA were evaluated for their ability to detect anti-Fasciola hepatica antibodies in humans by using excretory-secretory antigen. The sensitivity of each method was 100%, but the specificity was 100% for ELISA and 97% for micro-ELISA. The micro-ELISA could be used as a screening assay and ELISA could be used as a confirmatory method for the serodiagnosis of human fascioliasis.

Potency analysis of inactivated vaccines for Aujeszky's disease virus (ADV), strain RC/79: lymphocyte stimulation in immunized pigs.

Mitogenic and antigenic lymphocyte stimulation was examined in pigs that had been immunized with 2 inactivated vaccines which had been prepared with Aujesky's disease virus (ADV), strain RC/79. One vaccine was partially purified by ultra-centrifugation (Vaccine A) the other one was not (Vaccine B). A second dose of vaccine had no influence over the blastogenic response when the lymphocytes were stimulated with phytohemoagglutinin (PHA). Lymphocyte response to the ADV antigen in the immunized pigs was significantly higher at day 30 post inoculation than at day 0 indicating that it was highly specific. Cellular antigens contained in the viral cultures produced a slight non-specific response as shown by a low increase in the levels of lymphocyte blastic transformation (LBT) in the control group at day 30 p.i., this group only received a non infected Vero cell suspension. This was the case in pigs that received vaccine A as well as in those that were vaccinated with vaccine B. Vaccine B contains a greater quantity of contaminating cellular antigens, since it is an impure vaccine. Such antigens could act as non-specific immunomodulators, potentiating cell-mediated immunity (CMI). This assay demonstrated that inactivated vaccines produced with VPR-RC/79, partially purified and unpurified are capable of inducing a humoral immune response. The blastogenic reaction of the peripheral blood lymphocytes to antigens of ADV strain RC/79, indicated that the employed immunogens also induced the CMI. Results indicate that the analyzed immunogens could be considered for the possible implementation of epidemiological measures, which imply the use of vaccines to prevent pseudo-rabies in Argentina.

Diagnosis of Enterocytozoon bieneusi by PCR in stool samples eluted from filter paper disks.

We report a PCR-based assay for the detection of Enterocytozoon bieneusi. We extracted DNA from feces which had been applied to filter paper disks and evaluated four preserving solutions. Infected specimens were identified by electrophoresis of amplicons from concentrated formalin-fixed samples and unconcentrated fresh feces. Our findings demonstrate that this methodology is effective for sample collection, mailing, and diagnosis of this pathogen.

Natural fertility in northeastern Mexico.

BACKGROUND: The aims of this study were as follows: 1) to describe the fertility of a sample of Mexican women (> or =45 years of age, married, not using any family planning methods, and residing in the Mexican state of Nuevo León); 2) to determine whether or not the distribution of completed family size fits the negative binomial distribution, as in other populations studied in the world, and 3) to assess the association between fertility and 10 explanatory variables. METHODS: A sample of 410 women was interviewed at and selected from seven medical units of the Instituto Mexicano del Seguro Social (IMSS). The women were grouped by their year of birth (1896-1925 and 1926-1955) and birthplace [persons whose four grandparents were born in northeastern Mexico (NE) and outside northeastern Mexico (Not-NE)]. A binomial negative distribution analysis was assessed. Multiple linear regression was used to assess association between fertility (transformed by the use of inverse hyperbolic sines) and 10 explanatory variables, including age at marriage, heterozygosity, individual admixture, wife's education, husband's education, wife's occupation, husband's occupation, and couple's residence zone, birth year, and birthplace. RESULTS: Completed fertility was only associated with age at marriage. This population showed a fertility pattern similar to those described in Venezuelan and Brazilian populations in 1950 and 1940, respectively. CONCLUSIONS: We conclude that before worldwide family planning programs, fertility was determined mainly by natural selection forces.